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migration/ram: Don't explicitly unprotect when unregistering uffd-wp 

When unregistering uffd-wp, older kernels before commit f369b07c86143
("mm/uffd:reset write protection when unregister with wp-mode") won't
clear the uffd-wp PTE bit. When re-registering uffd-wp, the previous
uffd-wp PTE bits would trigger again. With above commit, the kernel will
clear the uffd-wp PTE bits when unregistering itself.

Consequently, we'll clear the uffd-wp PTE bits now twice -- whereby we
don't care about clearing them at all: a new background snapshot will
re-register uffd-wp and re-protect all memory either way.

So let's skip the manual clearing of uffd-wp. If ever relevant, we
could clear conditionally in uffd_unregister_memory() -- we just need a
way to figure out more recent kernels.

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 13:45:26 +01:00 committed by Juan Quintela
parent 72ef3a3708
commit 7cc8e9e0fa
1 changed files with 0 additions and 9 deletions
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9
migration/ram.c
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@ -1918,12 +1918,6 @@ fail:
if ((block->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_change_protection(rs->uffdio_fd, block->host, block->max_length,
false, false);
uffd_unregister_memory(rs->uffdio_fd, block->host, block->max_length);
/* Cleanup flags and remove reference */
block->flags &= ~RAM_UF_WRITEPROTECT;
@ -1949,9 +1943,6 @@ void ram_write_tracking_stop(void)
if ((block->flags & RAM_UF_WRITEPROTECT) == 0) {
continue;
}
/* Remove protection and unregister all affected RAM blocks */
uffd_change_protection(rs->uffdio_fd, block->host, block->max_length,
false, false);
uffd_unregister_memory(rs->uffdio_fd, block->host, block->max_length);
trace_ram_write_tracking_ramblock_stop(block->idstr, block->page_size,