762 lines
22 KiB
C
762 lines
22 KiB
C
/*
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* Postcopy migration for RAM
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*
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* Copyright 2013-2015 Red Hat, Inc. and/or its affiliates
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*
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* Authors:
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* Dave Gilbert <dgilbert@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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*/
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/*
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* Postcopy is a migration technique where the execution flips from the
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* source to the destination before all the data has been copied.
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*/
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#include "qemu/osdep.h"
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#include <glib.h>
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#include "qemu-common.h"
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#include "migration/migration.h"
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#include "migration/postcopy-ram.h"
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#include "sysemu/sysemu.h"
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#include "sysemu/balloon.h"
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#include "qemu/error-report.h"
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#include "trace.h"
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/* Arbitrary limit on size of each discard command,
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* keeps them around ~200 bytes
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*/
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#define MAX_DISCARDS_PER_COMMAND 12
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struct PostcopyDiscardState {
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const char *ramblock_name;
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uint64_t offset; /* Bitmap entry for the 1st bit of this RAMBlock */
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uint16_t cur_entry;
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/*
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* Start and length of a discard range (bytes)
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*/
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uint64_t start_list[MAX_DISCARDS_PER_COMMAND];
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uint64_t length_list[MAX_DISCARDS_PER_COMMAND];
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unsigned int nsentwords;
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unsigned int nsentcmds;
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};
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/* Postcopy needs to detect accesses to pages that haven't yet been copied
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* across, and efficiently map new pages in, the techniques for doing this
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* are target OS specific.
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*/
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#if defined(__linux__)
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#include <poll.h>
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#include <sys/eventfd.h>
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#include <sys/mman.h>
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#include <sys/ioctl.h>
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#include <sys/syscall.h>
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#include <asm/types.h> /* for __u64 */
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#endif
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#if defined(__linux__) && defined(__NR_userfaultfd)
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#include <linux/userfaultfd.h>
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static bool ufd_version_check(int ufd)
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{
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struct uffdio_api api_struct;
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uint64_t ioctl_mask;
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api_struct.api = UFFD_API;
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api_struct.features = 0;
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if (ioctl(ufd, UFFDIO_API, &api_struct)) {
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error_report("postcopy_ram_supported_by_host: UFFDIO_API failed: %s",
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strerror(errno));
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return false;
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}
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ioctl_mask = (__u64)1 << _UFFDIO_REGISTER |
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(__u64)1 << _UFFDIO_UNREGISTER;
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if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
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error_report("Missing userfault features: %" PRIx64,
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(uint64_t)(~api_struct.ioctls & ioctl_mask));
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return false;
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}
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return true;
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}
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/*
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* Note: This has the side effect of munlock'ing all of RAM, that's
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* normally fine since if the postcopy succeeds it gets turned back on at the
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* end.
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*/
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bool postcopy_ram_supported_by_host(void)
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{
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long pagesize = getpagesize();
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int ufd = -1;
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bool ret = false; /* Error unless we change it */
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void *testarea = NULL;
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struct uffdio_register reg_struct;
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struct uffdio_range range_struct;
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uint64_t feature_mask;
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if ((1ul << qemu_target_page_bits()) > pagesize) {
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error_report("Target page size bigger than host page size");
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goto out;
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}
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ufd = syscall(__NR_userfaultfd, O_CLOEXEC);
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if (ufd == -1) {
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error_report("%s: userfaultfd not available: %s", __func__,
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strerror(errno));
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goto out;
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}
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/* Version and features check */
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if (!ufd_version_check(ufd)) {
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goto out;
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}
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/*
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* userfault and mlock don't go together; we'll put it back later if
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* it was enabled.
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*/
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if (munlockall()) {
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error_report("%s: munlockall: %s", __func__, strerror(errno));
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return -1;
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}
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/*
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* We need to check that the ops we need are supported on anon memory
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* To do that we need to register a chunk and see the flags that
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* are returned.
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*/
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testarea = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE |
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MAP_ANONYMOUS, -1, 0);
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if (testarea == MAP_FAILED) {
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error_report("%s: Failed to map test area: %s", __func__,
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strerror(errno));
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goto out;
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}
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g_assert(((size_t)testarea & (pagesize-1)) == 0);
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reg_struct.range.start = (uintptr_t)testarea;
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reg_struct.range.len = pagesize;
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reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
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if (ioctl(ufd, UFFDIO_REGISTER, ®_struct)) {
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error_report("%s userfault register: %s", __func__, strerror(errno));
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goto out;
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}
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range_struct.start = (uintptr_t)testarea;
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range_struct.len = pagesize;
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if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) {
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error_report("%s userfault unregister: %s", __func__, strerror(errno));
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goto out;
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}
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feature_mask = (__u64)1 << _UFFDIO_WAKE |
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(__u64)1 << _UFFDIO_COPY |
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(__u64)1 << _UFFDIO_ZEROPAGE;
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if ((reg_struct.ioctls & feature_mask) != feature_mask) {
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error_report("Missing userfault map features: %" PRIx64,
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(uint64_t)(~reg_struct.ioctls & feature_mask));
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goto out;
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}
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/* Success! */
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ret = true;
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out:
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if (testarea) {
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munmap(testarea, pagesize);
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}
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if (ufd != -1) {
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close(ufd);
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}
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return ret;
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}
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/**
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* postcopy_ram_discard_range: Discard a range of memory.
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* We can assume that if we've been called postcopy_ram_hosttest returned true.
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*
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* @mis: Current incoming migration state.
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* @start, @length: range of memory to discard.
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*
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* returns: 0 on success.
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*/
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int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
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size_t length)
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{
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trace_postcopy_ram_discard_range(start, length);
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if (madvise(start, length, MADV_DONTNEED)) {
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error_report("%s MADV_DONTNEED: %s", __func__, strerror(errno));
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return -1;
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}
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return 0;
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}
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/*
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* Setup an area of RAM so that it *can* be used for postcopy later; this
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* must be done right at the start prior to pre-copy.
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* opaque should be the MIS.
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*/
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static int init_range(const char *block_name, void *host_addr,
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ram_addr_t offset, ram_addr_t length, void *opaque)
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{
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MigrationIncomingState *mis = opaque;
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trace_postcopy_init_range(block_name, host_addr, offset, length);
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/*
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* We need the whole of RAM to be truly empty for postcopy, so things
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* like ROMs and any data tables built during init must be zero'd
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* - we're going to get the copy from the source anyway.
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* (Precopy will just overwrite this data, so doesn't need the discard)
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*/
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if (postcopy_ram_discard_range(mis, host_addr, length)) {
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return -1;
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}
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return 0;
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}
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/*
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* At the end of migration, undo the effects of init_range
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* opaque should be the MIS.
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*/
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static int cleanup_range(const char *block_name, void *host_addr,
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ram_addr_t offset, ram_addr_t length, void *opaque)
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{
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MigrationIncomingState *mis = opaque;
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struct uffdio_range range_struct;
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trace_postcopy_cleanup_range(block_name, host_addr, offset, length);
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/*
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* We turned off hugepage for the precopy stage with postcopy enabled
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* we can turn it back on now.
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*/
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qemu_madvise(host_addr, length, QEMU_MADV_HUGEPAGE);
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/*
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* We can also turn off userfault now since we should have all the
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* pages. It can be useful to leave it on to debug postcopy
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* if you're not sure it's always getting every page.
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*/
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range_struct.start = (uintptr_t)host_addr;
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range_struct.len = length;
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if (ioctl(mis->userfault_fd, UFFDIO_UNREGISTER, &range_struct)) {
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error_report("%s: userfault unregister %s", __func__, strerror(errno));
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return -1;
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}
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return 0;
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}
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/*
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* Initialise postcopy-ram, setting the RAM to a state where we can go into
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* postcopy later; must be called prior to any precopy.
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* called from arch_init's similarly named ram_postcopy_incoming_init
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*/
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int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
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{
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if (qemu_ram_foreach_block(init_range, mis)) {
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return -1;
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}
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return 0;
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}
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/*
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* At the end of a migration where postcopy_ram_incoming_init was called.
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*/
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int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
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{
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trace_postcopy_ram_incoming_cleanup_entry();
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if (mis->have_fault_thread) {
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uint64_t tmp64;
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if (qemu_ram_foreach_block(cleanup_range, mis)) {
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return -1;
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}
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/*
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* Tell the fault_thread to exit, it's an eventfd that should
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* currently be at 0, we're going to increment it to 1
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*/
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tmp64 = 1;
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if (write(mis->userfault_quit_fd, &tmp64, 8) == 8) {
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trace_postcopy_ram_incoming_cleanup_join();
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qemu_thread_join(&mis->fault_thread);
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} else {
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/* Not much we can do here, but may as well report it */
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error_report("%s: incrementing userfault_quit_fd: %s", __func__,
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strerror(errno));
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}
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trace_postcopy_ram_incoming_cleanup_closeuf();
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close(mis->userfault_fd);
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close(mis->userfault_quit_fd);
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mis->have_fault_thread = false;
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}
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qemu_balloon_inhibit(false);
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if (enable_mlock) {
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if (os_mlock() < 0) {
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error_report("mlock: %s", strerror(errno));
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/*
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* It doesn't feel right to fail at this point, we have a valid
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* VM state.
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*/
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}
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}
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postcopy_state_set(POSTCOPY_INCOMING_END);
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migrate_send_rp_shut(mis, qemu_file_get_error(mis->from_src_file) != 0);
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if (mis->postcopy_tmp_page) {
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munmap(mis->postcopy_tmp_page, getpagesize());
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mis->postcopy_tmp_page = NULL;
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}
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trace_postcopy_ram_incoming_cleanup_exit();
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return 0;
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}
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/*
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* Disable huge pages on an area
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*/
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static int nhp_range(const char *block_name, void *host_addr,
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ram_addr_t offset, ram_addr_t length, void *opaque)
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{
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trace_postcopy_nhp_range(block_name, host_addr, offset, length);
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/*
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* Before we do discards we need to ensure those discards really
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* do delete areas of the page, even if THP thinks a hugepage would
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* be a good idea, so force hugepages off.
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*/
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qemu_madvise(host_addr, length, QEMU_MADV_NOHUGEPAGE);
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return 0;
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}
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/*
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* Userfault requires us to mark RAM as NOHUGEPAGE prior to discard
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* however leaving it until after precopy means that most of the precopy
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* data is still THPd
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*/
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int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
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{
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if (qemu_ram_foreach_block(nhp_range, mis)) {
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return -1;
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}
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postcopy_state_set(POSTCOPY_INCOMING_DISCARD);
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return 0;
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}
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/*
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* Mark the given area of RAM as requiring notification to unwritten areas
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* Used as a callback on qemu_ram_foreach_block.
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* host_addr: Base of area to mark
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* offset: Offset in the whole ram arena
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* length: Length of the section
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* opaque: MigrationIncomingState pointer
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* Returns 0 on success
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*/
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static int ram_block_enable_notify(const char *block_name, void *host_addr,
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ram_addr_t offset, ram_addr_t length,
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void *opaque)
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{
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MigrationIncomingState *mis = opaque;
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struct uffdio_register reg_struct;
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reg_struct.range.start = (uintptr_t)host_addr;
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reg_struct.range.len = length;
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reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
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/* Now tell our userfault_fd that it's responsible for this area */
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if (ioctl(mis->userfault_fd, UFFDIO_REGISTER, ®_struct)) {
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error_report("%s userfault register: %s", __func__, strerror(errno));
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return -1;
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}
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return 0;
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}
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/*
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* Handle faults detected by the USERFAULT markings
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*/
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static void *postcopy_ram_fault_thread(void *opaque)
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{
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MigrationIncomingState *mis = opaque;
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struct uffd_msg msg;
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int ret;
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size_t hostpagesize = getpagesize();
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RAMBlock *rb = NULL;
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RAMBlock *last_rb = NULL; /* last RAMBlock we sent part of */
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trace_postcopy_ram_fault_thread_entry();
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qemu_sem_post(&mis->fault_thread_sem);
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while (true) {
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ram_addr_t rb_offset;
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ram_addr_t in_raspace;
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struct pollfd pfd[2];
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/*
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* We're mainly waiting for the kernel to give us a faulting HVA,
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* however we can be told to quit via userfault_quit_fd which is
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* an eventfd
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*/
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pfd[0].fd = mis->userfault_fd;
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pfd[0].events = POLLIN;
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pfd[0].revents = 0;
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pfd[1].fd = mis->userfault_quit_fd;
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pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */
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pfd[1].revents = 0;
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if (poll(pfd, 2, -1 /* Wait forever */) == -1) {
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error_report("%s: userfault poll: %s", __func__, strerror(errno));
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break;
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}
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if (pfd[1].revents) {
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trace_postcopy_ram_fault_thread_quit();
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break;
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}
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ret = read(mis->userfault_fd, &msg, sizeof(msg));
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if (ret != sizeof(msg)) {
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if (errno == EAGAIN) {
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/*
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* if a wake up happens on the other thread just after
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* the poll, there is nothing to read.
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*/
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continue;
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}
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if (ret < 0) {
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error_report("%s: Failed to read full userfault message: %s",
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__func__, strerror(errno));
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break;
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} else {
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error_report("%s: Read %d bytes from userfaultfd expected %zd",
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__func__, ret, sizeof(msg));
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break; /* Lost alignment, don't know what we'd read next */
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}
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}
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if (msg.event != UFFD_EVENT_PAGEFAULT) {
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error_report("%s: Read unexpected event %ud from userfaultfd",
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__func__, msg.event);
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continue; /* It's not a page fault, shouldn't happen */
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}
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rb = qemu_ram_block_from_host(
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(void *)(uintptr_t)msg.arg.pagefault.address,
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true, &in_raspace, &rb_offset);
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if (!rb) {
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error_report("postcopy_ram_fault_thread: Fault outside guest: %"
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PRIx64, (uint64_t)msg.arg.pagefault.address);
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break;
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}
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rb_offset &= ~(hostpagesize - 1);
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trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address,
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qemu_ram_get_idstr(rb),
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rb_offset);
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/*
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* Send the request to the source - we want to request one
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* of our host page sizes (which is >= TPS)
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*/
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if (rb != last_rb) {
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last_rb = rb;
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migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
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rb_offset, hostpagesize);
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} else {
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/* Save some space */
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migrate_send_rp_req_pages(mis, NULL,
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rb_offset, hostpagesize);
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}
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}
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trace_postcopy_ram_fault_thread_exit();
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return NULL;
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}
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int postcopy_ram_enable_notify(MigrationIncomingState *mis)
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{
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/* Open the fd for the kernel to give us userfaults */
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mis->userfault_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
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if (mis->userfault_fd == -1) {
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error_report("%s: Failed to open userfault fd: %s", __func__,
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strerror(errno));
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return -1;
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}
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/*
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* Although the host check already tested the API, we need to
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* do the check again as an ABI handshake on the new fd.
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*/
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if (!ufd_version_check(mis->userfault_fd)) {
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return -1;
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}
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/* Now an eventfd we use to tell the fault-thread to quit */
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mis->userfault_quit_fd = eventfd(0, EFD_CLOEXEC);
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if (mis->userfault_quit_fd == -1) {
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error_report("%s: Opening userfault_quit_fd: %s", __func__,
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strerror(errno));
|
|
close(mis->userfault_fd);
|
|
return -1;
|
|
}
|
|
|
|
qemu_sem_init(&mis->fault_thread_sem, 0);
|
|
qemu_thread_create(&mis->fault_thread, "postcopy/fault",
|
|
postcopy_ram_fault_thread, mis, QEMU_THREAD_JOINABLE);
|
|
qemu_sem_wait(&mis->fault_thread_sem);
|
|
qemu_sem_destroy(&mis->fault_thread_sem);
|
|
mis->have_fault_thread = true;
|
|
|
|
/* Mark so that we get notified of accesses to unwritten areas */
|
|
if (qemu_ram_foreach_block(ram_block_enable_notify, mis)) {
|
|
return -1;
|
|
}
|
|
|
|
/*
|
|
* Ballooning can mark pages as absent while we're postcopying
|
|
* that would cause false userfaults.
|
|
*/
|
|
qemu_balloon_inhibit(true);
|
|
|
|
trace_postcopy_ram_enable_notify();
|
|
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Place a host page (from) at (host) atomically
|
|
* returns 0 on success
|
|
*/
|
|
int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from)
|
|
{
|
|
struct uffdio_copy copy_struct;
|
|
|
|
copy_struct.dst = (uint64_t)(uintptr_t)host;
|
|
copy_struct.src = (uint64_t)(uintptr_t)from;
|
|
copy_struct.len = getpagesize();
|
|
copy_struct.mode = 0;
|
|
|
|
/* copy also acks to the kernel waking the stalled thread up
|
|
* TODO: We can inhibit that ack and only do it if it was requested
|
|
* which would be slightly cheaper, but we'd have to be careful
|
|
* of the order of updating our page state.
|
|
*/
|
|
if (ioctl(mis->userfault_fd, UFFDIO_COPY, ©_struct)) {
|
|
int e = errno;
|
|
error_report("%s: %s copy host: %p from: %p",
|
|
__func__, strerror(e), host, from);
|
|
|
|
return -e;
|
|
}
|
|
|
|
trace_postcopy_place_page(host);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Place a zero page at (host) atomically
|
|
* returns 0 on success
|
|
*/
|
|
int postcopy_place_page_zero(MigrationIncomingState *mis, void *host)
|
|
{
|
|
struct uffdio_zeropage zero_struct;
|
|
|
|
zero_struct.range.start = (uint64_t)(uintptr_t)host;
|
|
zero_struct.range.len = getpagesize();
|
|
zero_struct.mode = 0;
|
|
|
|
if (ioctl(mis->userfault_fd, UFFDIO_ZEROPAGE, &zero_struct)) {
|
|
int e = errno;
|
|
error_report("%s: %s zero host: %p",
|
|
__func__, strerror(e), host);
|
|
|
|
return -e;
|
|
}
|
|
|
|
trace_postcopy_place_page_zero(host);
|
|
return 0;
|
|
}
|
|
|
|
/*
|
|
* Returns a target page of memory that can be mapped at a later point in time
|
|
* using postcopy_place_page
|
|
* The same address is used repeatedly, postcopy_place_page just takes the
|
|
* backing page away.
|
|
* Returns: Pointer to allocated page
|
|
*
|
|
*/
|
|
void *postcopy_get_tmp_page(MigrationIncomingState *mis)
|
|
{
|
|
if (!mis->postcopy_tmp_page) {
|
|
mis->postcopy_tmp_page = mmap(NULL, getpagesize(),
|
|
PROT_READ | PROT_WRITE, MAP_PRIVATE |
|
|
MAP_ANONYMOUS, -1, 0);
|
|
if (!mis->postcopy_tmp_page) {
|
|
error_report("%s: %s", __func__, strerror(errno));
|
|
return NULL;
|
|
}
|
|
}
|
|
|
|
return mis->postcopy_tmp_page;
|
|
}
|
|
|
|
#else
|
|
/* No target OS support, stubs just fail */
|
|
bool postcopy_ram_supported_by_host(void)
|
|
{
|
|
error_report("%s: No OS support", __func__);
|
|
return false;
|
|
}
|
|
|
|
int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
|
|
{
|
|
error_report("postcopy_ram_incoming_init: No OS support");
|
|
return -1;
|
|
}
|
|
|
|
int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
|
|
{
|
|
assert(0);
|
|
return -1;
|
|
}
|
|
|
|
int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
|
|
size_t length)
|
|
{
|
|
assert(0);
|
|
return -1;
|
|
}
|
|
|
|
int postcopy_ram_prepare_discard(MigrationIncomingState *mis)
|
|
{
|
|
assert(0);
|
|
return -1;
|
|
}
|
|
|
|
int postcopy_ram_enable_notify(MigrationIncomingState *mis)
|
|
{
|
|
assert(0);
|
|
return -1;
|
|
}
|
|
|
|
int postcopy_place_page(MigrationIncomingState *mis, void *host, void *from)
|
|
{
|
|
assert(0);
|
|
return -1;
|
|
}
|
|
|
|
int postcopy_place_page_zero(MigrationIncomingState *mis, void *host)
|
|
{
|
|
assert(0);
|
|
return -1;
|
|
}
|
|
|
|
void *postcopy_get_tmp_page(MigrationIncomingState *mis)
|
|
{
|
|
assert(0);
|
|
return NULL;
|
|
}
|
|
|
|
#endif
|
|
|
|
/* ------------------------------------------------------------------------- */
|
|
|
|
/**
|
|
* postcopy_discard_send_init: Called at the start of each RAMBlock before
|
|
* asking to discard individual ranges.
|
|
*
|
|
* @ms: The current migration state.
|
|
* @offset: the bitmap offset of the named RAMBlock in the migration
|
|
* bitmap.
|
|
* @name: RAMBlock that discards will operate on.
|
|
*
|
|
* returns: a new PDS.
|
|
*/
|
|
PostcopyDiscardState *postcopy_discard_send_init(MigrationState *ms,
|
|
unsigned long offset,
|
|
const char *name)
|
|
{
|
|
PostcopyDiscardState *res = g_malloc0(sizeof(PostcopyDiscardState));
|
|
|
|
if (res) {
|
|
res->ramblock_name = name;
|
|
res->offset = offset;
|
|
}
|
|
|
|
return res;
|
|
}
|
|
|
|
/**
|
|
* postcopy_discard_send_range: Called by the bitmap code for each chunk to
|
|
* discard. May send a discard message, may just leave it queued to
|
|
* be sent later.
|
|
*
|
|
* @ms: Current migration state.
|
|
* @pds: Structure initialised by postcopy_discard_send_init().
|
|
* @start,@length: a range of pages in the migration bitmap in the
|
|
* RAM block passed to postcopy_discard_send_init() (length=1 is one page)
|
|
*/
|
|
void postcopy_discard_send_range(MigrationState *ms, PostcopyDiscardState *pds,
|
|
unsigned long start, unsigned long length)
|
|
{
|
|
size_t tp_bits = qemu_target_page_bits();
|
|
/* Convert to byte offsets within the RAM block */
|
|
pds->start_list[pds->cur_entry] = (start - pds->offset) << tp_bits;
|
|
pds->length_list[pds->cur_entry] = length << tp_bits;
|
|
trace_postcopy_discard_send_range(pds->ramblock_name, start, length);
|
|
pds->cur_entry++;
|
|
pds->nsentwords++;
|
|
|
|
if (pds->cur_entry == MAX_DISCARDS_PER_COMMAND) {
|
|
/* Full set, ship it! */
|
|
qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file,
|
|
pds->ramblock_name,
|
|
pds->cur_entry,
|
|
pds->start_list,
|
|
pds->length_list);
|
|
pds->nsentcmds++;
|
|
pds->cur_entry = 0;
|
|
}
|
|
}
|
|
|
|
/**
|
|
* postcopy_discard_send_finish: Called at the end of each RAMBlock by the
|
|
* bitmap code. Sends any outstanding discard messages, frees the PDS
|
|
*
|
|
* @ms: Current migration state.
|
|
* @pds: Structure initialised by postcopy_discard_send_init().
|
|
*/
|
|
void postcopy_discard_send_finish(MigrationState *ms, PostcopyDiscardState *pds)
|
|
{
|
|
/* Anything unsent? */
|
|
if (pds->cur_entry) {
|
|
qemu_savevm_send_postcopy_ram_discard(ms->to_dst_file,
|
|
pds->ramblock_name,
|
|
pds->cur_entry,
|
|
pds->start_list,
|
|
pds->length_list);
|
|
pds->nsentcmds++;
|
|
}
|
|
|
|
trace_postcopy_discard_send_finish(pds->ramblock_name, pds->nsentwords,
|
|
pds->nsentcmds);
|
|
|
|
g_free(pds);
|
|
}
|