* Andrey Gruzdev (andrey.gruz...@virtuozzo.com) wrote:
> 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.gruz...@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.gruz...@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)
Please split this stuff off into a separate patch; just make this one
the userfaultfd.[ch] and then a separate one for gluing it into ram.c
> +{
> +#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.gruz...@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");
Please include the errno (or strerror(errno))
> + 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;
> +}
It would be great if we could find a way to share this with
migration/postcopy-ram.c - this duplicates a lor of
request_ufd_features.
> +
> +/**
> + * 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",
PRIx64 for mode as well.
> + 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
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
