On 31.03.21 19:28, Andrey Gruzdev wrote:
This commit solves the issue with userfault_fd WP feature that
background snapshot is based on. For any never poluated or discarded
memory page, the UFFDIO_WRITEPROTECT ioctl() would skip updating
PTE for that page, thereby loosing WP setting for it.
So we need to pre-fault pages for each RAM block to be protected
before making a userfault_fd wr-protect ioctl().
Signed-off-by: Andrey Gruzdev <andrey.gruzdev@virtuozzo.com>
---
migration/migration.c | 6 ++++++
migration/ram.c | 48
+++++++++++++++++++++++++++++++++++++++++++
migration/ram.h | 1 +
3 files changed, 55 insertions(+)
diff --git a/migration/migration.c b/migration/migration.c
index be4729e7c8..71bce15a1b 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -3827,6 +3827,12 @@ static void *bg_migration_thread(void *opaque)
update_iteration_initial_status(s);
+ /*
+ * Prepare for tracking memory writes with UFFD-WP - populate
+ * RAM pages before protecting.
+ */
+ ram_write_tracking_prepare();
+
qemu_savevm_state_header(s->to_dst_file);
qemu_savevm_state_setup(s->to_dst_file);
diff --git a/migration/ram.c b/migration/ram.c
index 40e78952ad..24c8627214 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1560,6 +1560,54 @@ out:
return ret;
}
+/*
+ * ram_block_populate_pages: populate memory in the RAM block by
reading
+ * an integer from the beginning of each page.
+ *
+ * Since it's solely used for userfault_fd WP feature, here we just
+ * hardcode page size to qemu_real_host_page_size.
+ *
+ * @bs: RAM block to populate
+ */
+static void ram_block_populate_pages(RAMBlock *bs)
Usually we use "rb" or "block"; however migration/ram.c seems to do
things differently.
+{
+ char *ptr = (char *) bs->host;
+
+ for (ram_addr_t offset = 0; offset < bs->used_length;
+ offset += qemu_real_host_page_size) {
+ char tmp = *(ptr + offset);
^ missing empty line.
+ /* Don't optimize the read out */
+ asm volatile("" : "+r" (tmp));
+ }
Reviewed-by: David Hildenbrand <david@redhat.com>
and might want to add
Reported-by: David Hildenbrand <david@redhat.com>
(also to patch #2)