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migration/ram: Rely on used_length for uffd_change_protection() 

ram_mig_ram_block_resized() will abort migration (including background
snapshots) when resizing a RAMBlock. ram_block_populate_read() will only
populate RAM up to used_length, so at least for anonymous memory
protecting everything between used_length and max_length won't
actually be protected and is just a NOP.

So let's only protect everything up to used_length.

Note: it still makes sense to register uffd-wp for max_length, such
that RAM_UF_WRITEPROTECT is independent of a changing used_length.

Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
This commit is contained in:
David Hildenbrand 2023-01-05 13:45:27 +01:00 committed by Juan Quintela
parent 7cc8e9e0fa
commit 59bcc049c1
1 changed files with 1 additions and 1 deletions
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2
migration/ram.c
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@ -1901,7 +1901,7 @@ int ram_write_tracking_start(void)
/* Apply UFFD write protection to the block memory range */
if (uffd_change_protection(rs->uffdio_fd, block->host,
block->max_length, true, false)) {
block->used_length, true, false)) {
goto fail;
}