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[PATCH v4 2/6] introduce UFFD-WP low-level interface helpers
From: |
Andrey Gruzdev |
Subject: |
[PATCH v4 2/6] introduce UFFD-WP low-level interface helpers |
Date: |
Thu, 26 Nov 2020 18:17:30 +0300 |
Implemented support for the whole RAM block memory
protection/un-protection. Introduced higher level
ram_write_tracking_start() and ram_write_tracking_stop()
to start/stop tracking guest memory writes.
Signed-off-by: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
---
include/exec/memory.h | 7 ++
include/qemu/userfaultfd.h | 29 +++++
migration/ram.c | 120 +++++++++++++++++++++
migration/ram.h | 4 +
util/meson.build | 1 +
util/userfaultfd.c | 215 +++++++++++++++++++++++++++++++++++++
6 files changed, 376 insertions(+)
create mode 100644 include/qemu/userfaultfd.h
create mode 100644 util/userfaultfd.c
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 0f3e6bcd5e..3d798fce16 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -139,6 +139,13 @@ typedef struct IOMMUNotifier IOMMUNotifier;
/* RAM is a persistent kind memory */
#define RAM_PMEM (1 << 5)
+/*
+ * UFFDIO_WRITEPROTECT is used on this RAMBlock to
+ * support 'write-tracking' migration type.
+ * Implies ram_state->ram_wt_enabled.
+ */
+#define RAM_UF_WRITEPROTECT (1 << 6)
+
static inline void iommu_notifier_init(IOMMUNotifier *n, IOMMUNotify fn,
IOMMUNotifierFlag flags,
hwaddr start, hwaddr end,
diff --git a/include/qemu/userfaultfd.h b/include/qemu/userfaultfd.h
new file mode 100644
index 0000000000..fb843c76db
--- /dev/null
+++ b/include/qemu/userfaultfd.h
@@ -0,0 +1,29 @@
+/*
+ * Linux UFFD-WP support
+ *
+ * Copyright Virtuozzo GmbH, 2020
+ *
+ * Authors:
+ * Andrey Gruzdev <andrey.gruzdev@virtuozzo.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.
+ */
+
+#ifndef USERFAULTFD_H
+#define USERFAULTFD_H
+
+#include "qemu/osdep.h"
+#include "exec/hwaddr.h"
+#include <linux/userfaultfd.h>
+
+int uffd_create_fd(void);
+void uffd_close_fd(int uffd);
+int uffd_register_memory(int uffd, hwaddr start, hwaddr length,
+ bool track_missing, bool track_wp);
+int uffd_unregister_memory(int uffd, hwaddr start, hwaddr length);
+int uffd_protect_memory(int uffd, hwaddr start, hwaddr length, bool wp);
+int uffd_read_events(int uffd, struct uffd_msg *msgs, int count);
+bool uffd_poll_events(int uffd, int tmo);
+
+#endif /* USERFAULTFD_H */
diff --git a/migration/ram.c b/migration/ram.c
index 7811cde643..3adfd1948d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -56,6 +56,11 @@
#include "savevm.h"
#include "qemu/iov.h"
#include "multifd.h"
+#include "sysemu/runstate.h"
+
+#ifdef CONFIG_LINUX
+#include "qemu/userfaultfd.h"
+#endif
/***********************************************************/
/* ram save/restore */
@@ -298,6 +303,8 @@ struct RAMSrcPageRequest {
struct RAMState {
/* QEMUFile used for this migration */
QEMUFile *f;
+ /* UFFD file descriptor, used in 'write-tracking' migration */
+ int uffdio_fd;
/* Last block that we have visited searching for dirty pages */
RAMBlock *last_seen_block;
/* Last block from where we have sent data */
@@ -3788,6 +3795,119 @@ static int ram_resume_prepare(MigrationState *s, void
*opaque)
return 0;
}
+/*
+ * ram_write_tracking_start: start UFFD-WP memory tracking
+ *
+ * Returns 0 for success or negative value in case of error
+ *
+ */
+int ram_write_tracking_start(void)
+{
+#ifdef CONFIG_LINUX
+ int uffd;
+ RAMState *rs = ram_state;
+ RAMBlock *bs;
+
+ /* Open UFFD file descriptor */
+ uffd = uffd_create_fd();
+ if (uffd < 0) {
+ return uffd;
+ }
+ rs->uffdio_fd = uffd;
+
+ RAMBLOCK_FOREACH_NOT_IGNORED(bs) {
+ /* Nothing to do with read-only and MMIO-writable regions */
+ if (bs->mr->readonly || bs->mr->rom_device) {
+ continue;
+ }
+
+ bs->flags |= RAM_UF_WRITEPROTECT;
+ /* Register block memory with UFFD to track writes */
+ if (uffd_register_memory(rs->uffdio_fd, (hwaddr) bs->host,
+ bs->max_length, false, true)) {
+ goto fail;
+ }
+ /* Apply UFFD write protection to the block memory range */
+ if (uffd_protect_memory(rs->uffdio_fd, (hwaddr) bs->host,
+ bs->max_length, true)) {
+ goto fail;
+ }
+
+ info_report("UFFD-WP write-tracking enabled: "
+ "block_id=%s page_size=%zu start=%p length=%lu "
+ "romd_mode=%i ram=%i readonly=%i nonvolatile=%i rom_device=%i",
+ bs->idstr, bs->page_size, bs->host, bs->max_length,
+ bs->mr->romd_mode, bs->mr->ram, bs->mr->readonly,
+ bs->mr->nonvolatile, bs->mr->rom_device);
+ }
+
+ return 0;
+
+fail:
+ error_report("ram_write_tracking_start() failed: restoring initial memory
state");
+
+ RAMBLOCK_FOREACH_NOT_IGNORED(bs) {
+ if ((bs->flags & RAM_UF_WRITEPROTECT) == 0) {
+ continue;
+ }
+ /*
+ * In case some memory block failed to be write-protected
+ * remove protection and unregister all succeeded RAM blocks
+ */
+ uffd_protect_memory(rs->uffdio_fd, (hwaddr) bs->host, bs->max_length,
false);
+ uffd_unregister_memory(rs->uffdio_fd, (hwaddr) bs->host,
bs->max_length);
+ /* Cleanup flags */
+ bs->flags &= ~RAM_UF_WRITEPROTECT;
+ }
+
+ uffd_close_fd(uffd);
+ rs->uffdio_fd = -1;
+ return -1;
+#else
+ rs->uffdio_fd = -1;
+ error_setg(&migrate_get_current()->error,
+ "Background-snapshot not supported on non-Linux hosts");
+ return -1;
+#endif /* CONFIG_LINUX */
+}
+
+/**
+ * ram_write_tracking_stop: stop UFFD-WP memory tracking and remove protection
+ */
+void ram_write_tracking_stop(void)
+{
+#ifdef CONFIG_LINUX
+ RAMState *rs = ram_state;
+ RAMBlock *bs;
+ assert(rs->uffdio_fd >= 0);
+
+ RAMBLOCK_FOREACH_NOT_IGNORED(bs) {
+ if ((bs->flags & RAM_UF_WRITEPROTECT) == 0) {
+ continue;
+ }
+ /* Remove protection and unregister all affected RAM blocks */
+ uffd_protect_memory(rs->uffdio_fd, (hwaddr) bs->host, bs->max_length,
false);
+ uffd_unregister_memory(rs->uffdio_fd, (hwaddr) bs->host,
bs->max_length);
+ /* Cleanup flags */
+ bs->flags &= ~RAM_UF_WRITEPROTECT;
+
+ info_report("UFFD-WP write-tracking disabled: "
+ "block_id=%s page_size=%zu start=%p length=%lu "
+ "romd_mode=%i ram=%i readonly=%i nonvolatile=%i rom_device=%i",
+ bs->idstr, bs->page_size, bs->host, bs->max_length,
+ bs->mr->romd_mode, bs->mr->ram, bs->mr->readonly,
+ bs->mr->nonvolatile, bs->mr->rom_device);
+ }
+
+ /* Finally close UFFD file descriptor */
+ uffd_close_fd(rs->uffdio_fd);
+ rs->uffdio_fd = -1;
+#else
+ error_setg(&migrate_get_current()->error,
+ "Background-snapshot not supported on non-Linux hosts");
+#endif /* CONFIG_LINUX */
+}
+
static SaveVMHandlers savevm_ram_handlers = {
.save_setup = ram_save_setup,
.save_live_iterate = ram_save_iterate,
diff --git a/migration/ram.h b/migration/ram.h
index 011e85414e..0ec63e27ee 100644
--- a/migration/ram.h
+++ b/migration/ram.h
@@ -79,4 +79,8 @@ void colo_flush_ram_cache(void);
void colo_release_ram_cache(void);
void colo_incoming_start_dirty_log(void);
+/* Background snapshots */
+int ram_write_tracking_start(void);
+void ram_write_tracking_stop(void);
+
#endif
diff --git a/util/meson.build b/util/meson.build
index f359af0d46..c64bfe94b3 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -50,6 +50,7 @@ endif
if have_system
util_ss.add(when: 'CONFIG_GIO', if_true: [files('dbus.c'), gio])
+ util_ss.add(when: 'CONFIG_LINUX', if_true: files('userfaultfd.c'))
endif
if have_block
diff --git a/util/userfaultfd.c b/util/userfaultfd.c
new file mode 100644
index 0000000000..038953d7ed
--- /dev/null
+++ b/util/userfaultfd.c
@@ -0,0 +1,215 @@
+/*
+ * Linux UFFD-WP support
+ *
+ * Copyright Virtuozzo GmbH, 2020
+ *
+ * Authors:
+ * Andrey Gruzdev <andrey.gruzdev@virtuozzo.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.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/bitops.h"
+#include "qemu/error-report.h"
+#include "qemu/userfaultfd.h"
+#include <poll.h>
+#include <sys/syscall.h>
+#include <sys/ioctl.h>
+
+/**
+ * uffd_create_fd: create UFFD file descriptor
+ *
+ * Returns non-negative file descriptor or negative value in case of an error
+ */
+int uffd_create_fd(void)
+{
+ int uffd;
+ struct uffdio_api api_struct;
+ uint64_t ioctl_mask = BIT(_UFFDIO_REGISTER) | BIT(_UFFDIO_UNREGISTER);
+
+ uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
+ if (uffd < 0) {
+ error_report("uffd_create_fd() failed: UFFD not supported");
+ return -1;
+ }
+
+ api_struct.api = UFFD_API;
+ api_struct.features = UFFD_FEATURE_PAGEFAULT_FLAG_WP;
+ if (ioctl(uffd, UFFDIO_API, &api_struct)) {
+ error_report("uffd_create_fd() failed: "
+ "API version not supported version=%llx errno=%i",
+ api_struct.api, errno);
+ goto fail;
+ }
+
+ if ((api_struct.ioctls & ioctl_mask) != ioctl_mask) {
+ error_report("uffd_create_fd() failed: "
+ "PAGEFAULT_FLAG_WP feature missing");
+ goto fail;
+ }
+
+ return uffd;
+
+fail:
+ close(uffd);
+ return -1;
+}
+
+/**
+ * uffd_close_fd: close UFFD file descriptor
+ *
+ * @uffd: UFFD file descriptor
+ */
+void uffd_close_fd(int uffd)
+{
+ assert(uffd >= 0);
+ close(uffd);
+}
+
+/**
+ * uffd_register_memory: register memory range with UFFD
+ *
+ * Returns 0 in case of success, negative value on error
+ *
+ * @uffd: UFFD file descriptor
+ * @start: starting virtual address of memory range
+ * @length: length of memory range
+ * @track_missing: generate events on missing-page faults
+ * @track_wp: generate events on write-protected-page faults
+ */
+int uffd_register_memory(int uffd, hwaddr start, hwaddr length,
+ bool track_missing, bool track_wp)
+{
+ struct uffdio_register uffd_register;
+
+ uffd_register.range.start = start;
+ uffd_register.range.len = length;
+ uffd_register.mode = (track_missing ? UFFDIO_REGISTER_MODE_MISSING : 0) |
+ (track_wp ? UFFDIO_REGISTER_MODE_WP : 0);
+
+ if (ioctl(uffd, UFFDIO_REGISTER, &uffd_register)) {
+ error_report("uffd_register_memory() failed: "
+ "start=%0"PRIx64" len=%"PRIu64" mode=%llu errno=%i",
+ start, length, uffd_register.mode, errno);
+ return -1;
+ }
+
+ return 0;
+}
+
+/**
+ * uffd_unregister_memory: un-register memory range with UFFD
+ *
+ * Returns 0 in case of success, negative value on error
+ *
+ * @uffd: UFFD file descriptor
+ * @start: starting virtual address of memory range
+ * @length: length of memory range
+ */
+int uffd_unregister_memory(int uffd, hwaddr start, hwaddr length)
+{
+ struct uffdio_range uffd_range;
+
+ uffd_range.start = start;
+ uffd_range.len = length;
+
+ if (ioctl(uffd, UFFDIO_UNREGISTER, &uffd_range)) {
+ error_report("uffd_unregister_memory() failed: "
+ "start=%0"PRIx64" len=%"PRIu64" errno=%i",
+ start, length, errno);
+ return -1;
+ }
+
+ return 0;
+}
+
+/**
+ * uffd_protect_memory: protect/unprotect memory range for writes with UFFD
+ *
+ * Returns 0 on success or negative value in case of error
+ *
+ * @uffd: UFFD file descriptor
+ * @start: starting virtual address of memory range
+ * @length: length of memory range
+ * @wp: write-protect/unprotect
+ */
+int uffd_protect_memory(int uffd, hwaddr start, hwaddr length, bool wp)
+{
+ struct uffdio_writeprotect uffd_writeprotect;
+ int res;
+
+ uffd_writeprotect.range.start = start;
+ uffd_writeprotect.range.len = length;
+ uffd_writeprotect.mode = (wp ? UFFDIO_WRITEPROTECT_MODE_WP : 0);
+
+ do {
+ res = ioctl(uffd, UFFDIO_WRITEPROTECT, &uffd_writeprotect);
+ } while (res < 0 && errno == EINTR);
+ if (res < 0) {
+ error_report("uffd_protect_memory() failed: "
+ "start=%0"PRIx64" len=%"PRIu64" mode=%llu errno=%i",
+ start, length, uffd_writeprotect.mode, errno);
+ return -1;
+ }
+
+ return 0;
+}
+
+/**
+ * uffd_read_events: read pending UFFD events
+ *
+ * Returns number of fetched messages, 0 if non is available or
+ * negative value in case of an error
+ *
+ * @uffd: UFFD file descriptor
+ * @msgs: pointer to message buffer
+ * @count: number of messages that can fit in the buffer
+ */
+int uffd_read_events(int uffd, struct uffd_msg *msgs, int count)
+{
+ ssize_t res;
+ do {
+ res = read(uffd, msgs, count * sizeof(struct uffd_msg));
+ } while (res < 0 && errno == EINTR);
+
+ if ((res < 0 && errno == EAGAIN)) {
+ return 0;
+ }
+ if (res < 0) {
+ error_report("uffd_read_events() failed: errno=%i", errno);
+ return -1;
+ }
+
+ return (int) (res / sizeof(struct uffd_msg));
+}
+
+/**
+ * uffd_poll_events: poll UFFD file descriptor for read
+ *
+ * Returns true if events are available for read, false otherwise
+ *
+ * @uffd: UFFD file descriptor
+ * @tmo: timeout in milliseconds, 0 for non-blocking operation,
+ * negative value for infinite wait
+ */
+bool uffd_poll_events(int uffd, int tmo)
+{
+ int res;
+ struct pollfd poll_fd = { .fd = uffd, .events = POLLIN, .revents = 0 };
+
+ do {
+ res = poll(&poll_fd, 1, tmo);
+ } while (res < 0 && errno == EINTR);
+
+ if (res == 0) {
+ return false;
+ }
+ if (res < 0) {
+ error_report("uffd_poll_events() failed: errno=%i", errno);
+ return false;
+ }
+
+ return (poll_fd.revents & POLLIN) != 0;
+}
--
2.25.1
[PATCH v4 3/6] support UFFD write fault processing in ram_save_iterate(), Andrey Gruzdev, 2020/11/26
[PATCH v4 4/6] implementation of background snapshot thread, Andrey Gruzdev, 2020/11/26