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[Qemu-devel] [PATCH v5 40/45] Postcopy; Handle userfault requests
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[Qemu-devel] [PATCH v5 40/45] Postcopy; Handle userfault requests |
Date: |
Wed, 25 Feb 2015 16:52:03 +0000 |
From: "Dr. David Alan Gilbert" <address@hidden>
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.
Signed-off-by: Dr. David Alan Gilbert <address@hidden>
---
include/migration/migration.h | 4 +
migration/postcopy-ram.c | 217 ++++++++++++++++++++++++++++++++++++++++--
trace-events | 12 +++
3 files changed, 223 insertions(+), 10 deletions(-)
diff --git a/include/migration/migration.h b/include/migration/migration.h
index 139bb1b..cec064f 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -86,11 +86,15 @@ struct MigrationIncomingState {
PostcopyState postcopy_state;
+ 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 *return_path;
QemuMutex rp_mutex; /* We send replies from multiple threads */
PostcopyPMI postcopy_pmi;
diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index 86fa5a0..abc039e 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -47,6 +47,8 @@ struct PostcopyDiscardState {
*/
#if defined(__linux__)
+#include <poll.h>
+#include <sys/eventfd.h>
#include <sys/mman.h>
#include <sys/ioctl.h>
#include <sys/types.h>
@@ -264,7 +266,7 @@ void postcopy_pmi_dump(MigrationIncomingState *mis)
void postcopy_hook_early_receive(MigrationIncomingState *mis,
size_t bitmap_index)
{
- if (mis->postcopy_state == POSTCOPY_INCOMING_ADVISE) {
+ if (postcopy_state_get(mis) == POSTCOPY_INCOMING_ADVISE) {
/*
* If we're in precopy-advise mode we need to track received pages even
* though we don't need to place pages atomically yet.
@@ -489,15 +491,40 @@ 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_area, mis)) {
- return -1;
+ trace_postcopy_ram_incoming_cleanup_entry();
+
+ if (mis->have_fault_thread) {
+ uint64_t tmp64;
+
+ if (qemu_ram_foreach_block(cleanup_area, mis)) {
+ return -1;
+ }
+ /*
+ * Tell the fault_thread to exit, it's an eventfd that should
+ * currently be at 0, we're going to inc 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 */
+ perror("incing userfault_quit_fd");
+ }
+ trace_postcopy_ram_incoming_cleanup_closeuf();
+ close(mis->userfault_fd);
+ close(mis->userfault_quit_fd);
+ mis->have_fault_thread = false;
}
+ postcopy_state_set(mis, POSTCOPY_INCOMING_END);
+ migrate_send_rp_shut(mis, qemu_file_get_error(mis->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;
}
@@ -531,36 +558,206 @@ static int ram_block_enable_notify(const char
*block_name, void *host_addr,
}
/*
+ * Tell the kernel that we've now got some memory it previously asked for.
+ */
+static int ack_userfault(MigrationIncomingState *mis, void *start, size_t len)
+{
+ struct uffdio_range range_struct;
+
+ range_struct.start = (uint64_t)(uintptr_t)start;
+ range_struct.len = (uint64_t)len;
+
+ errno = 0;
+ if (ioctl(mis->userfault_fd, UFFDIO_WAKE, &range_struct)) {
+ int e = errno;
+
+ if (e == ENOENT) {
+ /* Kernel said it wasn't waiting - one case where this can
+ * happen is where two threads triggered the userfault
+ * and we receive the page and ack it just after we received
+ * the 2nd request and that ends up deciding it should ack it
+ * We could optimise it out, but it's rare.
+ */
+ /*fprintf(stderr, "ack_userfault: %p/%zx ENOENT\n", start, len); */
+ return 0;
+ }
+ error_report("postcopy_ram: Failed to notify kernel for %p/%zx (%d)",
+ start, len, e);
+ return -e;
+ }
+
+ return 0;
+}
+
+/*
* Handle faults detected by the USERFAULT markings
*/
static void *postcopy_ram_fault_thread(void *opaque)
{
MigrationIncomingState *mis = (MigrationIncomingState *)opaque;
-
- fprintf(stderr, "postcopy_ram_fault_thread\n");
- /* TODO: In later patch */
+ uint64_t hostaddr; /* The kernel always gives us 64 bit, not a pointer */
+ int ret;
+ size_t hostpagesize = getpagesize();
+ RAMBlock *rb = NULL;
+ RAMBlock *last_rb = NULL; /* last RAMBlock we sent part of */
+ uint8_t *local_tmp_page;
+
+ trace_postcopy_ram_fault_thread_entry();
qemu_sem_post(&mis->fault_thread_sem);
- while (1) {
- /* TODO: In later patch */
+
+ local_tmp_page = mmap(NULL, getpagesize(),
+ PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS,
+ -1, 0);
+ if (!local_tmp_page) {
+ perror("mapping local tmp page");
+ return NULL;
}
+ if (madvise(local_tmp_page, getpagesize(), MADV_DONTFORK)) {
+ munmap(local_tmp_page, getpagesize());
+ perror("postcpy local page DONTFORK");
+ return NULL;
+ }
+
+ while (true) {
+ PostcopyPMIState old_state, tmp_state;
+ ram_addr_t rb_offset;
+ ram_addr_t in_raspace;
+ unsigned long bitmap_index;
+ 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) {
+ perror("userfault poll");
+ break;
+ }
+
+ if (pfd[1].revents) {
+ trace_postcopy_ram_fault_thread_quit();
+ break;
+ }
+
+ ret = read(mis->userfault_fd, &hostaddr, sizeof(hostaddr));
+ if (ret != sizeof(hostaddr)) {
+ if (ret < 0) {
+ perror("Failed to read full userfault hostaddr");
+ break;
+ } else {
+ error_report("%s: Read %d bytes from userfaultfd expected %zd",
+ __func__, ret, sizeof(hostaddr));
+ break; /* Lost alignment, don't know what we'd read next */
+ }
+ }
+
+ rb = qemu_ram_block_from_host((void *)(uintptr_t)hostaddr, true,
+ &in_raspace, &rb_offset, &bitmap_index);
+ if (!rb) {
+ error_report("postcopy_ram_fault_thread: Fault outside guest: %"
+ PRIx64, hostaddr);
+ break;
+ }
+ trace_postcopy_ram_fault_thread_request(hostaddr, bitmap_index,
+ qemu_ram_get_idstr(rb),
+ rb_offset);
+
+ tmp_state = postcopy_pmi_get_state(mis, bitmap_index);
+ do {
+ old_state = tmp_state;
+
+ switch (old_state) {
+ case POSTCOPY_PMI_REQUESTED:
+ /* Do nothing - it's already requested */
+ break;
+
+ case POSTCOPY_PMI_RECEIVED:
+ /* Already arrived - no state change, just kick the kernel */
+ trace_postcopy_ram_fault_thread_notify_pre(hostaddr);
+ if (ack_userfault(mis,
+ (void *)((uintptr_t)hostaddr
+ & ~(hostpagesize - 1)),
+ hostpagesize)) {
+ assert(0);
+ }
+ break;
+
+ case POSTCOPY_PMI_MISSING:
+ tmp_state = postcopy_pmi_change_state(mis, bitmap_index,
+ old_state, POSTCOPY_PMI_REQUESTED);
+ if (tmp_state == POSTCOPY_PMI_MISSING) {
+ /*
+ * 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);
+ }
+ } /* else it just arrived from the source and the kernel will
+ be kicked during the receive */
+ break;
+ }
+ } while (tmp_state != old_state);
+ }
+ munmap(local_tmp_page, getpagesize());
+ 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);
+ if (mis->userfault_fd == -1) {
+ perror("Failed to open userfault fd");
+ 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) {
+ perror("Opening userfault_quit_fd");
+ 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;
}
diff --git a/trace-events b/trace-events
index 16a91d9..d955a28 100644
--- a/trace-events
+++ b/trace-events
@@ -1498,6 +1498,18 @@ postcopy_discard_send_finish(const char *ramblock, int
nwords, int ncmds) "%s ma
postcopy_cleanup_area(const char *ramblock, void *host_addr, size_t offset,
size_t length) "%s: %p offset=%zx length=%zx"
postcopy_init_area(const char *ramblock, void *host_addr, size_t offset,
size_t length) "%s: %p offset=%zx length=%zx"
postcopy_place_page(unsigned long offset, void *host_addr, bool all_zero, int
old_state) "offset=%lx host=%p all_zero=%d old_state=%d"
+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, unsigned long index,
const char *ramblock, size_t offset) "Request for HVA=%" PRIx64 " index=%lx
rb=%s offset=%zx"
+postcopy_ram_fault_thread_notify_pre(uint64_t hostaddr) "%" PRIx64
+postcopy_ram_fault_thread_notify_zero(void *hostaddr) "%p"
+postcopy_ram_fault_thread_notify_zero_ack(void *hostaddr, unsigned long
bitmap_index) "%p %lx"
+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"
--
2.1.0
- [Qemu-devel] [PATCH v5 30/45] Postcopy: Postcopy startup in migration thread, (continued)
- [Qemu-devel] [PATCH v5 30/45] Postcopy: Postcopy startup in migration thread, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 31/45] Postcopy end in migration_thread, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 32/45] Page request: Add MIG_RP_CMD_REQ_PAGES reverse command, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 33/45] Page request: Process incoming page request, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 34/45] Page request: Consume pages off the post-copy queue, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 35/45] postcopy_ram.c: place_page and helpers, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 36/45] Postcopy: Use helpers to map pages during migration, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 38/45] Don't sync dirty bitmaps in postcopy, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 39/45] Host page!=target page: Cleanup bitmaps, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 37/45] qemu_ram_block_from_host, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 40/45] Postcopy; Handle userfault requests,
Dr. David Alan Gilbert (git) <=
- [Qemu-devel] [PATCH v5 42/45] postcopy: Wire up loadvm_postcopy_handle_{run, end} commands, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 41/45] Start up a postcopy/listener thread ready for incoming page data, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 43/45] End of migration for postcopy, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 45/45] Inhibit ballooning during postcopy, Dr. David Alan Gilbert (git), 2015/02/25
- [Qemu-devel] [PATCH v5 44/45] Disable mlock around incoming postcopy, Dr. David Alan Gilbert (git), 2015/02/25