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[PULL 10/26] migration/ram: Rely on used_length for uffd_change_protection()

Juan Quintela posted 26 patches 3 years ago

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Maintainers: "Marc-André Lureau" <marcandre.lureau@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Juan Quintela <quintela@redhat.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, Alex Williamson <alex.williamson@redhat.com>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, Yanan Wang <wangyanan55@huawei.com>, Halil Pasic <pasic@linux.ibm.com>, Christian Borntraeger <borntraeger@linux.ibm.com>, Eric Farman <farman@linux.ibm.com>, Richard Henderson <richard.henderson@linaro.org>, David Hildenbrand <david@redhat.com>, Ilya Leoshkevich <iii@linux.ibm.com>, Thomas Huth <thuth@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>, "Daniel P. Berrangé" <berrange@redhat.com>, Stefan Hajnoczi <stefanha@redhat.com>, Fam Zheng <fam@euphon.net>, Eric Blake <eblake@redhat.com>, Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>, John Snow <jsnow@redhat.com>, Laurent Vivier <lvivier@redhat.com>, Stefan Berger <stefanb@linux.vnet.ibm.com>, Coiby Xu <Coiby.Xu@gmail.com>

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[PULL 10/26] migration/ram: Rely on used_length for uffd_change_protection()

Posted by Juan Quintela 3 years ago

From: David Hildenbrand <david@redhat.com>

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>
---
 migration/ram.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/migration/ram.c b/migration/ram.c
index efaae07dd8..a6956c9e7d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -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;
         }
 
-- 
2.39.1