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>
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@ -1918,12 +1918,6 @@ fail:
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if ((block->flags & RAM_UF_WRITEPROTECT) == 0) {
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continue;
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}
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/*
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* In case some memory block failed to be write-protected
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* remove protection and unregister all succeeded RAM blocks
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*/
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uffd_change_protection(rs->uffdio_fd, block->host, block->max_length,
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false, false);
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uffd_unregister_memory(rs->uffdio_fd, block->host, block->max_length);
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/* Cleanup flags and remove reference */
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block->flags &= ~RAM_UF_WRITEPROTECT;
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@ -1949,9 +1943,6 @@ void ram_write_tracking_stop(void)
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if ((block->flags & RAM_UF_WRITEPROTECT) == 0) {
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continue;
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}
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/* Remove protection and unregister all affected RAM blocks */
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uffd_change_protection(rs->uffdio_fd, block->host, block->max_length,
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false, false);
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uffd_unregister_memory(rs->uffdio_fd, block->host, block->max_length);
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trace_ram_write_tracking_ramblock_stop(block->idstr, block->page_size,
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