qemu/migration/postcopy-ram.c
Dr. David Alan Gilbert f0a227ade4 postcopy: ram_enable_notify to switch on userfault
Mark the area of RAM as 'userfault'
Start up a fault-thread to handle any userfaults we might receive
from it (to be filled in later)

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
2015-11-10 15:00:27 +01:00

457 lines
13 KiB
C

/*
* Postcopy migration for RAM
*
* Copyright 2013-2015 Red Hat, Inc. and/or its affiliates
*
* Authors:
* Dave Gilbert <dgilbert@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*
*/
/*
* Postcopy is a migration technique where the execution flips from the
* source to the destination before all the data has been copied.
*/
#include <glib.h>
#include <stdio.h>
#include <unistd.h>
#include "qemu-common.h"
#include "migration/migration.h"
#include "migration/postcopy-ram.h"
#include "sysemu/sysemu.h"
#include "qemu/error-report.h"
#include "trace.h"
/* Arbitrary limit on size of each discard command,
* keeps them around ~200 bytes
*/
#define MAX_DISCARDS_PER_COMMAND 12
struct PostcopyDiscardState {
const char *ramblock_name;
uint64_t offset; /* Bitmap entry for the 1st bit of this RAMBlock */
uint16_t cur_entry;
/*
* Start and length of a discard range (bytes)
*/
uint64_t start_list[MAX_DISCARDS_PER_COMMAND];
uint64_t length_list[MAX_DISCARDS_PER_COMMAND];
unsigned int nsentwords;
unsigned int nsentcmds;
};
/* Postcopy needs to detect accesses to pages that haven't yet been copied
* across, and efficiently map new pages in, the techniques for doing this
* are target OS specific.
*/
#if defined(__linux__)
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <sys/syscall.h>
#include <sys/types.h>
#include <asm/types.h> /* for __u64 */
#endif
#if defined(__linux__) && defined(__NR_userfaultfd)
#include <linux/userfaultfd.h>
static bool ufd_version_check(int ufd)
{
struct uffdio_api api_struct;
uint64_t ioctl_mask;
api_struct.api = UFFD_API;
api_struct.features = 0;
if (ioctl(ufd, UFFDIO_API, &api_struct)) {
error_report("postcopy_ram_supported_by_host: UFFDIO_API failed: %s",
strerror(errno));
return false;
}
ioctl_mask = (__u64)1 << _UFFDIO_REGISTER |
(__u64)1 << _UFFDIO_UNREGISTER;
if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
error_report("Missing userfault features: %" PRIx64,
(uint64_t)(~api_struct.ioctls & ioctl_mask));
return false;
}
return true;
}
bool postcopy_ram_supported_by_host(void)
{
long pagesize = getpagesize();
int ufd = -1;
bool ret = false; /* Error unless we change it */
void *testarea = NULL;
struct uffdio_register reg_struct;
struct uffdio_range range_struct;
uint64_t feature_mask;
if ((1ul << qemu_target_page_bits()) > pagesize) {
error_report("Target page size bigger than host page size");
goto out;
}
ufd = syscall(__NR_userfaultfd, O_CLOEXEC);
if (ufd == -1) {
error_report("%s: userfaultfd not available: %s", __func__,
strerror(errno));
goto out;
}
/* Version and features check */
if (!ufd_version_check(ufd)) {
goto out;
}
/*
* We need to check that the ops we need are supported on anon memory
* To do that we need to register a chunk and see the flags that
* are returned.
*/
testarea = mmap(NULL, pagesize, PROT_READ | PROT_WRITE, MAP_PRIVATE |
MAP_ANONYMOUS, -1, 0);
if (testarea == MAP_FAILED) {
error_report("%s: Failed to map test area: %s", __func__,
strerror(errno));
goto out;
}
g_assert(((size_t)testarea & (pagesize-1)) == 0);
reg_struct.range.start = (uintptr_t)testarea;
reg_struct.range.len = pagesize;
reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
if (ioctl(ufd, UFFDIO_REGISTER, &reg_struct)) {
error_report("%s userfault register: %s", __func__, strerror(errno));
goto out;
}
range_struct.start = (uintptr_t)testarea;
range_struct.len = pagesize;
if (ioctl(ufd, UFFDIO_UNREGISTER, &range_struct)) {
error_report("%s userfault unregister: %s", __func__, strerror(errno));
goto out;
}
feature_mask = (__u64)1 << _UFFDIO_WAKE |
(__u64)1 << _UFFDIO_COPY |
(__u64)1 << _UFFDIO_ZEROPAGE;
if ((reg_struct.ioctls & feature_mask) != feature_mask) {
error_report("Missing userfault map features: %" PRIx64,
(uint64_t)(~reg_struct.ioctls & feature_mask));
goto out;
}
/* Success! */
ret = true;
out:
if (testarea) {
munmap(testarea, pagesize);
}
if (ufd != -1) {
close(ufd);
}
return ret;
}
/**
* postcopy_ram_discard_range: Discard a range of memory.
* We can assume that if we've been called postcopy_ram_hosttest returned true.
*
* @mis: Current incoming migration state.
* @start, @length: range of memory to discard.
*
* returns: 0 on success.
*/
int postcopy_ram_discard_range(MigrationIncomingState *mis, uint8_t *start,
size_t length)
{
trace_postcopy_ram_discard_range(start, length);
if (madvise(start, length, MADV_DONTNEED)) {
error_report("%s MADV_DONTNEED: %s", __func__, strerror(errno));
return -1;
}
return 0;
}
/*
* Setup an area of RAM so that it *can* be used for postcopy later; this
* must be done right at the start prior to pre-copy.
* opaque should be the MIS.
*/
static int init_range(const char *block_name, void *host_addr,
ram_addr_t offset, ram_addr_t length, void *opaque)
{
MigrationIncomingState *mis = opaque;
trace_postcopy_init_range(block_name, host_addr, offset, length);
/*
* We need the whole of RAM to be truly empty for postcopy, so things
* like ROMs and any data tables built during init must be zero'd
* - we're going to get the copy from the source anyway.
* (Precopy will just overwrite this data, so doesn't need the discard)
*/
if (postcopy_ram_discard_range(mis, host_addr, length)) {
return -1;
}
return 0;
}
/*
* At the end of migration, undo the effects of init_range
* opaque should be the MIS.
*/
static int cleanup_range(const char *block_name, void *host_addr,
ram_addr_t offset, ram_addr_t length, void *opaque)
{
MigrationIncomingState *mis = opaque;
struct uffdio_range range_struct;
trace_postcopy_cleanup_range(block_name, host_addr, offset, length);
/*
* We turned off hugepage for the precopy stage with postcopy enabled
* we can turn it back on now.
*/
#ifdef MADV_HUGEPAGE
if (madvise(host_addr, length, MADV_HUGEPAGE)) {
error_report("%s HUGEPAGE: %s", __func__, strerror(errno));
return -1;
}
#endif
/*
* We can also turn off userfault now since we should have all the
* pages. It can be useful to leave it on to debug postcopy
* if you're not sure it's always getting every page.
*/
range_struct.start = (uintptr_t)host_addr;
range_struct.len = length;
if (ioctl(mis->userfault_fd, UFFDIO_UNREGISTER, &range_struct)) {
error_report("%s: userfault unregister %s", __func__, strerror(errno));
return -1;
}
return 0;
}
/*
* Initialise postcopy-ram, setting the RAM to a state where we can go into
* postcopy later; must be called prior to any precopy.
* called from arch_init's similarly named ram_postcopy_incoming_init
*/
int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t ram_pages)
{
if (qemu_ram_foreach_block(init_range, mis)) {
return -1;
}
return 0;
}
/*
* At the end of a migration where postcopy_ram_incoming_init was called.
*/
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;
}
return 0;
}
/*
* Mark the given area of RAM as requiring notification to unwritten areas
* Used as a callback on qemu_ram_foreach_block.
* host_addr: Base of area to mark
* offset: Offset in the whole ram arena
* length: Length of the section
* opaque: MigrationIncomingState pointer
* Returns 0 on success
*/
static int ram_block_enable_notify(const char *block_name, void *host_addr,
ram_addr_t offset, ram_addr_t length,
void *opaque)
{
MigrationIncomingState *mis = opaque;
struct uffdio_register reg_struct;
reg_struct.range.start = (uintptr_t)host_addr;
reg_struct.range.len = length;
reg_struct.mode = UFFDIO_REGISTER_MODE_MISSING;
/* Now tell our userfault_fd that it's responsible for this area */
if (ioctl(mis->userfault_fd, UFFDIO_REGISTER, &reg_struct)) {
error_report("%s userfault register: %s", __func__, strerror(errno));
return -1;
}
return 0;
}
/*
* Handle faults detected by the USERFAULT markings
*/
static void *postcopy_ram_fault_thread(void *opaque)
{
MigrationIncomingState *mis = opaque;
fprintf(stderr, "postcopy_ram_fault_thread\n");
/* TODO: In later patch */
qemu_sem_post(&mis->fault_thread_sem);
while (1) {
/* TODO: In later patch */
}
return NULL;
}
int postcopy_ram_enable_notify(MigrationIncomingState *mis)
{
/* Create the fault handler thread and wait for it to be ready */
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);
/* Mark so that we get notified of accesses to unwritten areas */
if (qemu_ram_foreach_block(ram_block_enable_notify, mis)) {
return -1;
}
return 0;
}
#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_enable_notify(MigrationIncomingState *mis)
{
assert(0);
return -1;
}
#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->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->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);
}