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[PATCH v1 9/9] vfio: Disable only uncoordinated discards

From: David Hildenbrand
Subject: [PATCH v1 9/9] vfio: Disable only uncoordinated discards
Date: Thu, 19 Nov 2020 16:39:18 +0100

We support coordinated discarding of RAM using the RamDiscardMgr. Let's
unlock support for coordinated discards, keeping uncoordinated discards
(e.g., via virtio-balloon) disabled.

This unlocks virtio-mem + vfio. Note that vfio used via "nvme://" by the
block layer has to be implemented/unlocked separately. For now,
virtio-mem only supports x86-64 - spapr IOMMUs are not tested/affected.

Note: The block size of a virtio-mem device has to be set to sane sizes,
depending on the maximum hotplug size - to not run out of vfio mappings.
The default virtio-mem block size is usually in the range of a couple of
MBs. The maximum number of mapping is 64k, shared with other users.
Assume you want to hotplug 256GB using virtio-mem - the block size would
have to be set to at least 8 MiB (resulting in 32768 separate mappings).

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Auger Eric <eric.auger@redhat.com>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Marek Kedzierski <mkedzier@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
 hw/vfio/common.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/hw/vfio/common.c b/hw/vfio/common.c
index 0d950186f1..4063a8382f 100644
--- a/hw/vfio/common.c
+++ b/hw/vfio/common.c
@@ -1967,8 +1967,10 @@ static int vfio_connect_container(VFIOGroup *group, 
AddressSpace *as,
      * new memory, it will not yet set ram_block_discard_set_required() and
      * therefore, neither stops us here or deals with the sudden memory
      * consumption of inflated memory.
+     *
+     * We do support discarding of memory coordinated via the RamDiscardMgr.
-    ret = ram_block_discard_disable(true);
+    ret = ram_block_uncoordinated_discard_disable(true);
     if (ret) {
         error_setg_errno(errp, -ret, "Cannot set discarding of RAM broken");
         return ret;
@@ -2144,7 +2146,7 @@ close_fd_exit:
-    ram_block_discard_disable(false);
+    ram_block_uncoordinated_discard_disable(false);
     return ret;
@@ -2266,7 +2268,7 @@ void vfio_put_group(VFIOGroup *group)
     if (!group->ram_block_discard_allowed) {
-        ram_block_discard_disable(false);
+        ram_block_uncoordinated_discard_disable(false);
@@ -2320,7 +2322,7 @@ int vfio_get_device(VFIOGroup *group, const char *name,
         if (!group->ram_block_discard_allowed) {
             group->ram_block_discard_allowed = true;
-            ram_block_discard_disable(false);
+            ram_block_uncoordinated_discard_disable(false);

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