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Postcopy; Handle userfault requests 

userfaultfd is a Linux syscall that gives an fd that receives a stream
of notifications of accesses to pages registered with it and allows
the program to acknowledge those stalls and tell the accessing
thread to carry on.

We convert the requests from the kernel into messages back to the
source asking for the pages.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
Dr. David Alan Gilbert 2015-11-05 18:11:17 +00:00 committed by Juan Quintela
parent 4ed023ce2a
commit c4faeed231
3 changed files with 158 additions and 9 deletions
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3
include/migration/migration.h
View File

@ -89,11 +89,14 @@ struct MigrationIncomingState {
*/
QemuEvent main_thread_load_event;
bool have_fault_thread;
QemuThread fault_thread;
QemuSemaphore fault_thread_sem;
/* For the kernel to send us notifications */
int userfault_fd;
/* To tell the fault_thread to quit */
int userfault_quit_fd;
QEMUFile *to_src_file;
QemuMutex rp_mutex; /* We send replies from multiple threads */
void *postcopy_tmp_page;

155
migration/postcopy-ram.c
View File

@ -51,6 +51,8 @@ struct PostcopyDiscardState {
*/
#if defined(__linux__)
#include <poll.h>
#include <sys/eventfd.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
@ -267,15 +269,41 @@ int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
*/
int postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
{
/* TODO: Join the fault thread once we're sure it will exit */
if (qemu_ram_foreach_block(cleanup_range, mis)) {
return -1;
trace_postcopy_ram_incoming_cleanup_entry();
if (mis->have_fault_thread) {
uint64_t tmp64;
if (qemu_ram_foreach_block(cleanup_range, mis)) {
return -1;
}
/*
* Tell the fault_thread to exit, it's an eventfd that should
* currently be at 0, we're going to increment it to 1
*/
tmp64 = 1;
if (write(mis->userfault_quit_fd, &tmp64, 8) == 8) {
trace_postcopy_ram_incoming_cleanup_join();
qemu_thread_join(&mis->fault_thread);
} else {
/* Not much we can do here, but may as well report it */
error_report("%s: incrementing userfault_quit_fd: %s", __func__,
strerror(errno));
}
trace_postcopy_ram_incoming_cleanup_closeuf();
close(mis->userfault_fd);
close(mis->userfault_quit_fd);
mis->have_fault_thread = false;
}
postcopy_state_set(POSTCOPY_INCOMING_END);
migrate_send_rp_shut(mis, qemu_file_get_error(mis->from_src_file) != 0);
if (mis->postcopy_tmp_page) {
munmap(mis->postcopy_tmp_page, getpagesize());
mis->postcopy_tmp_page = NULL;
}
trace_postcopy_ram_incoming_cleanup_exit();
return 0;
}
@ -314,31 +342,140 @@ static int ram_block_enable_notify(const char *block_name, void *host_addr,
static void *postcopy_ram_fault_thread(void *opaque)
{
MigrationIncomingState *mis = opaque;
struct uffd_msg msg;
int ret;
size_t hostpagesize = getpagesize();
RAMBlock *rb = NULL;
RAMBlock *last_rb = NULL; /* last RAMBlock we sent part of */
fprintf(stderr, "postcopy_ram_fault_thread\n");
/* TODO: In later patch */
trace_postcopy_ram_fault_thread_entry();
qemu_sem_post(&mis->fault_thread_sem);
while (1) {
/* TODO: In later patch */
}
while (true) {
ram_addr_t rb_offset;
ram_addr_t in_raspace;
struct pollfd pfd[2];
/*
* We're mainly waiting for the kernel to give us a faulting HVA,
* however we can be told to quit via userfault_quit_fd which is
* an eventfd
*/
pfd[0].fd = mis->userfault_fd;
pfd[0].events = POLLIN;
pfd[0].revents = 0;
pfd[1].fd = mis->userfault_quit_fd;
pfd[1].events = POLLIN; /* Waiting for eventfd to go positive */
pfd[1].revents = 0;
if (poll(pfd, 2, -1 /* Wait forever */) == -1) {
error_report("%s: userfault poll: %s", __func__, strerror(errno));
break;
}
if (pfd[1].revents) {
trace_postcopy_ram_fault_thread_quit();
break;
}
ret = read(mis->userfault_fd, &msg, sizeof(msg));
if (ret != sizeof(msg)) {
if (errno == EAGAIN) {
/*
* if a wake up happens on the other thread just after
* the poll, there is nothing to read.
*/
continue;
}
if (ret < 0) {
error_report("%s: Failed to read full userfault message: %s",
__func__, strerror(errno));
break;
} else {
error_report("%s: Read %d bytes from userfaultfd expected %zd",
__func__, ret, sizeof(msg));
break; /* Lost alignment, don't know what we'd read next */
}
}
if (msg.event != UFFD_EVENT_PAGEFAULT) {
error_report("%s: Read unexpected event %ud from userfaultfd",
__func__, msg.event);
continue; /* It's not a page fault, shouldn't happen */
}
rb = qemu_ram_block_from_host(
(void *)(uintptr_t)msg.arg.pagefault.address,
true, &in_raspace, &rb_offset);
if (!rb) {
error_report("postcopy_ram_fault_thread: Fault outside guest: %"
PRIx64, (uint64_t)msg.arg.pagefault.address);
break;
}
rb_offset &= ~(hostpagesize - 1);
trace_postcopy_ram_fault_thread_request(msg.arg.pagefault.address,
qemu_ram_get_idstr(rb),
rb_offset);
/*
* Send the request to the source - we want to request one
* of our host page sizes (which is >= TPS)
*/
if (rb != last_rb) {
last_rb = rb;
migrate_send_rp_req_pages(mis, qemu_ram_get_idstr(rb),
rb_offset, hostpagesize);
} else {
/* Save some space */
migrate_send_rp_req_pages(mis, NULL,
rb_offset, hostpagesize);
}
}
trace_postcopy_ram_fault_thread_exit();
return NULL;
}
int postcopy_ram_enable_notify(MigrationIncomingState *mis)
{
/* Create the fault handler thread and wait for it to be ready */
/* Open the fd for the kernel to give us userfaults */
mis->userfault_fd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
if (mis->userfault_fd == -1) {
error_report("%s: Failed to open userfault fd: %s", __func__,
strerror(errno));
return -1;
}
/*
* Although the host check already tested the API, we need to
* do the check again as an ABI handshake on the new fd.
*/
if (!ufd_version_check(mis->userfault_fd)) {
return -1;
}
/* Now an eventfd we use to tell the fault-thread to quit */
mis->userfault_quit_fd = eventfd(0, EFD_CLOEXEC);
if (mis->userfault_quit_fd == -1) {
error_report("%s: Opening userfault_quit_fd: %s", __func__,
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;
}
trace_postcopy_ram_enable_notify();
return 0;
}

9
trace-events
View File

@ -1554,6 +1554,15 @@ postcopy_cleanup_range(const char *ramblock, void *host_addr, size_t offset, siz
postcopy_init_range(const char *ramblock, void *host_addr, size_t offset, size_t length) "%s: %p offset=%zx length=%zx"
postcopy_place_page(void *host_addr) "host=%p"
postcopy_place_page_zero(void *host_addr) "host=%p"
postcopy_ram_enable_notify(void) ""
postcopy_ram_fault_thread_entry(void) ""
postcopy_ram_fault_thread_exit(void) ""
postcopy_ram_fault_thread_quit(void) ""
postcopy_ram_fault_thread_request(uint64_t hostaddr, const char *ramblock, size_t offset) "Request for HVA=%" PRIx64 " rb=%s offset=%zx"
postcopy_ram_incoming_cleanup_closeuf(void) ""
postcopy_ram_incoming_cleanup_entry(void) ""
postcopy_ram_incoming_cleanup_exit(void) ""
postcopy_ram_incoming_cleanup_join(void) ""
# kvm-all.c
kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"