7197fb4058
Since commit 8561c9244d "exec: allocate PROT_NONE pages on top of
RAM", it is no longer possible to back guest RAM with hugepages on ppc64
hosts:
mmap(NULL, 285212672, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) =
0x3fff57000000
mmap(0x3fff57000000, 268435456, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED, 19, 0) = -1 EBUSY (Device or resource busy)
This is because on ppc64, Linux fixes a page size for a virtual address
at mmap time, so we can't switch a range of memory from anonymous
small pages to hugetlbs with MAP_FIXED.
See commit d0f13e3c20b6fb73ccb467bdca97fa7cf5a574cd
("[POWERPC] Introduce address space "slices"") in Linux
history for the details.
Detect this and create the PROT_NONE mapping using the same fd.
Naturally, this makes the guard page bigger with hugetlbfs.
Based on patch by Greg Kurz.
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Tested-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
111 lines
3.0 KiB
C
111 lines
3.0 KiB
C
/*
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* Support for RAM backed by mmaped host memory.
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*
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* Copyright (c) 2015 Red Hat, Inc.
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*
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* Authors:
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* Michael S. Tsirkin <mst@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or
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* later. See the COPYING file in the top-level directory.
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*/
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#include <qemu/mmap-alloc.h>
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#include <sys/types.h>
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#include <sys/mman.h>
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#include <assert.h>
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#define HUGETLBFS_MAGIC 0x958458f6
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#ifdef CONFIG_LINUX
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#include <sys/vfs.h>
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#endif
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size_t qemu_fd_getpagesize(int fd)
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{
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#ifdef CONFIG_LINUX
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struct statfs fs;
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int ret;
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if (fd != -1) {
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do {
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ret = fstatfs(fd, &fs);
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} while (ret != 0 && errno == EINTR);
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if (ret == 0 && fs.f_type == HUGETLBFS_MAGIC) {
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return fs.f_bsize;
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}
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}
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#endif
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return getpagesize();
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}
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void *qemu_ram_mmap(int fd, size_t size, size_t align, bool shared)
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{
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/*
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* Note: this always allocates at least one extra page of virtual address
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* space, even if size is already aligned.
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*/
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size_t total = size + align;
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#if defined(__powerpc64__) && defined(__linux__)
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/* On ppc64 mappings in the same segment (aka slice) must share the same
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* page size. Since we will be re-allocating part of this segment
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* from the supplied fd, we should make sure to use the same page size,
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* unless we are using the system page size, in which case anonymous memory
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* is OK. Use align as a hint for the page size.
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* In this case, set MAP_NORESERVE to avoid allocating backing store memory.
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*/
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int anonfd = fd == -1 || qemu_fd_getpagesize(fd) == getpagesize() ? -1 : fd;
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int flags = anonfd == -1 ? MAP_ANONYMOUS : MAP_NORESERVE;
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void *ptr = mmap(0, total, PROT_NONE, flags | MAP_PRIVATE, anonfd, 0);
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#else
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void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
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#endif
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size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
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void *ptr1;
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if (ptr == MAP_FAILED) {
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return MAP_FAILED;
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}
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/* Make sure align is a power of 2 */
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assert(!(align & (align - 1)));
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/* Always align to host page size */
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assert(align >= getpagesize());
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ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
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MAP_FIXED |
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(fd == -1 ? MAP_ANONYMOUS : 0) |
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(shared ? MAP_SHARED : MAP_PRIVATE),
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fd, 0);
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if (ptr1 == MAP_FAILED) {
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munmap(ptr, total);
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return MAP_FAILED;
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}
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ptr += offset;
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total -= offset;
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if (offset > 0) {
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munmap(ptr - offset, offset);
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}
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/*
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* Leave a single PROT_NONE page allocated after the RAM block, to serve as
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* a guard page guarding against potential buffer overflows.
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*/
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if (total > size + getpagesize()) {
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munmap(ptr + size + getpagesize(), total - size - getpagesize());
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}
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return ptr;
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}
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void qemu_ram_munmap(void *ptr, size_t size)
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{
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if (ptr) {
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/* Unmap both the RAM block and the guard page */
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munmap(ptr, size + getpagesize());
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}
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}
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