util/vfio-helpers.c: Use ram_block_discard_disable() in qemu_vfio_open_pci()

Currently, when using "nvme://" for a block device, like
    -drive file=nvme://0000:01:00.0/1,if=none,id=drive0 \
    -device virtio-blk,drive=drive0 \

VFIO may pin all guest memory, and discarding of RAM no longer works as
expected. I was able to reproduce this easily with my
    01:00.0 Non-Volatile memory controller: Samsung Electronics Co Ltd
            NVMe SSD Controller SM981/PM981/PM983

Similar to common VFIO, we have to disable it, making sure that:
a) virtio-balloon won't discard any memory ("silently disabled")
b) virtio-mem and nvme:// run mutually exclusive

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Alex Williamson <alex.williamson@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.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>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20201116105947.9194-1-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/stubs/ram-block.c b/stubs/ram-block.c
index 73c0a3e..1081976 100644
--- a/stubs/ram-block.c
+++ b/stubs/ram-block.c
@@ -1,6 +1,7 @@
 #include "qemu/osdep.h"
 #include "exec/ramlist.h"
 #include "exec/cpu-common.h"
+#include "exec/memory.h"
 
 void *qemu_ram_get_host_addr(RAMBlock *rb)
 {
@@ -29,3 +30,8 @@ int qemu_ram_foreach_block(RAMBlockIterFunc func, void *opaque)
 {
     return 0;
 }
+
+int ram_block_discard_disable(bool state)
+{
+    return 0;
+}