[PATCH v3 19/49] kvm: Make kvm_convert_memory() obey ram_block_discard_is_enabled()

[Michael Roth]

Some subsystems like VFIO might disable ram block discard for
uncoordinated cases. Since kvm_convert_memory()/guest_memfd don't
implement a RamDiscardManager handler to convey discard operations to
various listeners like VFIO. Because of this, sequences like the
following can result due to stale IOMMU mappings:

  - convert page shared->private
  - discard shared page
  - convert page private->shared
  - new page is allocated
  - issue DMA operations against that shared page

Address this by taking ram_block_discard_is_enabled() into account when
deciding whether or not to discard pages.

Signed-off-by: Michael Roth <michael.roth@amd.com>
---
 accel/kvm/kvm-all.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 53ce4f091e..6ae03c880f 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2962,10 +2962,14 @@ static int kvm_convert_memory(hwaddr start, hwaddr 
size, bool to_private)
                 */
                 return 0;
             } else {
-                ret = ram_block_discard_range(rb, offset, size);
+                ret = ram_block_discard_is_disabled()
+                      ? ram_block_discard_range(rb, offset, size)
+                      : 0;
             }
         } else {
-            ret = ram_block_discard_guest_memfd_range(rb, offset, size);
+            ret = ram_block_discard_is_disabled()
+                  ? ram_block_discard_guest_memfd_range(rb, offset, size)
+                  : 0;
         }
     } else {
         error_report("Convert non guest_memfd backed memory region "
-- 
2.25.1