* Andrey Gruzdev (andrey.gruz...@virtuozzo.com) wrote:
> In this particular implementation the same single migration
> thread is responsible for both normal linear dirty page
> migration and procesing UFFD page fault events.
>
> Processing write faults includes reading UFFD file descriptor,
> finding respective RAM block and saving faulting page to
> the migration stream. After page has been saved, write protection
> can be removed. Since asynchronous version of qemu_put_buffer()
> is expected to be used to save pages, we also have to flush
> migraion stream prior to un-protecting saved memory range.
>
> Write protection is being removed for any previously protected
> memory chunk that has hit the migration stream. That's valid
> for pages from linear page scan along with write fault pages.
>
> Signed-off-by: Andrey Gruzdev <andrey.gruz...@virtuozzo.com>
> ---
> migration/ram.c | 124 ++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 115 insertions(+), 9 deletions(-)
>
> diff --git a/migration/ram.c b/migration/ram.c
> index 7f273c9996..08a1d7a252 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -314,6 +314,8 @@ struct RAMState {
> ram_addr_t last_page;
> /* last ram version we have seen */
> uint32_t last_version;
> + /* 'write-tracking' migration is enabled */
> + bool ram_wt_enabled;
> /* We are in the first round */
> bool ram_bulk_stage;
> /* The free page optimization is enabled */
> @@ -574,8 +576,6 @@ static int uffd_protect_memory(int uffd, hwaddr start,
> hwaddr length, bool wp)
> return 0;
> }
>
> -__attribute__ ((unused))
> -static int uffd_read_events(int uffd, struct uffd_msg *msgs, int count);
> __attribute__ ((unused))
> static bool uffd_poll_events(int uffd, int tmo);
>
> @@ -1929,6 +1929,86 @@ static int ram_save_host_page(RAMState *rs,
> PageSearchStatus *pss,
> return pages;
> }
>
> +/**
> + * ram_find_block_by_host_address: find RAM block containing host page
> + *
> + * Returns true if RAM block is found and pss->block/page are
> + * pointing to the given host page, false in case of an error
> + *
> + * @rs: current RAM state
> + * @pss: page-search-status structure
> + */
> +static bool ram_find_block_by_host_address(RAMState *rs, PageSearchStatus
> *pss,
> + hwaddr page_address)
> +{
> + bool found = false;
> +
> + pss->block = rs->last_seen_block;
> + do {
> + if (page_address >= (hwaddr) pss->block->host &&
> + (page_address + TARGET_PAGE_SIZE) <=
> + ((hwaddr) pss->block->host + pss->block->used_length)) {
> + pss->page = (unsigned long)
> + ((page_address - (hwaddr) pss->block->host) >>
> TARGET_PAGE_BITS);
> + found = true;
> + break;
> + }
> +
> + pss->block = QLIST_NEXT_RCU(pss->block, next);
> + if (!pss->block) {
> + /* Hit the end of the list */
> + pss->block = QLIST_FIRST_RCU(&ram_list.blocks);
> + }
> + } while (pss->block != rs->last_seen_block);
> +
> + rs->last_seen_block = pss->block;
> + /*
> + * Since we are in the same loop with ram_find_and_save_block(),
> + * need to reset pss->complete_round after switching to
> + * other block/page in pss.
> + */
> + pss->complete_round = false;
> +
> + return found;
> +}
> +
> +/**
> + * get_fault_page: try to get next UFFD write fault page and, if pending
> fault
> + * is found, put info about RAM block and block page into pss structure
> + *
> + * Returns true in case of UFFD write fault detected, false otherwise
> + *
> + * @rs: current RAM state
> + * @pss: page-search-status structure
> + *
> + */
> +static bool get_fault_page(RAMState *rs, PageSearchStatus *pss)
> +{
> + struct uffd_msg uffd_msg;
> + hwaddr page_address;
> + int res;
> +
> + if (!rs->ram_wt_enabled) {
> + return false;
> + }
> +
> + res = uffd_read_events(rs->uffdio_fd, &uffd_msg, 1);
> + if (res <= 0) {
> + return false;
> + }
> +
> + page_address = uffd_msg.arg.pagefault.address;
> + if (!ram_find_block_by_host_address(rs, pss, page_address)) {
> + /* In case we couldn't find respective block, just unprotect
> faulting page */
> + uffd_protect_memory(rs->uffdio_fd, page_address, TARGET_PAGE_SIZE,
> false);
> + error_report("ram_find_block_by_host_address() failed:
> address=0x%0lx",
> + page_address);
> + return false;
> + }
> +
> + return true;
> +}
> +
> /**
> * ram_find_and_save_block: finds a dirty page and sends it to f
> *
> @@ -1955,25 +2035,50 @@ static int ram_find_and_save_block(RAMState *rs, bool
> last_stage)
> return pages;
> }
>
> + if (!rs->last_seen_block) {
> + rs->last_seen_block = QLIST_FIRST_RCU(&ram_list.blocks);
> + }
> pss.block = rs->last_seen_block;
> pss.page = rs->last_page;
> pss.complete_round = false;
>
> - if (!pss.block) {
> - pss.block = QLIST_FIRST_RCU(&ram_list.blocks);
> - }
> -
> do {
> + ram_addr_t page;
> + ram_addr_t page_to;
> +
> again = true;
> - found = get_queued_page(rs, &pss);
> -
> + /* In case of 'write-tracking' migration we first try
> + * to poll UFFD and get write page fault event */
> + found = get_fault_page(rs, &pss);
> + if (!found) {
> + /* No trying to fetch something from the priority queue */
> + found = get_queued_page(rs, &pss);
> + }
> if (!found) {
> /* priority queue empty, so just search for something dirty */
> found = find_dirty_block(rs, &pss, &again);
> }
>
> if (found) {
> + page = pss.page;
> pages = ram_save_host_page(rs, &pss, last_stage);
> + page_to = pss.page;
> +
> + /* Check if page is from UFFD-managed region */
> + if (pss.block->flags & RAM_UF_WRITEPROTECT) {
> + hwaddr page_address = (hwaddr) pss.block->host +
> + ((hwaddr) page << TARGET_PAGE_BITS);
> + hwaddr run_length = (hwaddr) (page_to - page + 1) <<
> TARGET_PAGE_BITS;
> + int res;
> +
> + /* Flush async buffers before un-protect */
> + qemu_fflush(rs->f);
> + /* Un-protect memory range */
> + res = uffd_protect_memory(rs->uffdio_fd, page_address,
> run_length, false);
> + if (res < 0) {
> + break;
> + }
> + }
Please separate that out into a separate function.
Dave
> }
> } while (!pages && again);
>
> @@ -2086,7 +2191,8 @@ static void ram_state_reset(RAMState *rs)
> rs->last_sent_block = NULL;
> rs->last_page = 0;
> rs->last_version = ram_list.version;
> - rs->ram_bulk_stage = true;
> + rs->ram_wt_enabled = migrate_track_writes_ram();
> + rs->ram_bulk_stage = !rs->ram_wt_enabled;
> rs->fpo_enabled = false;
> }
>
> --
> 2.25.1
>
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
