intel_iommu: dma read/write draining support

Support DMA read/write draining should be easy for existing VT-d
emulation since the emulation itself does not have any request queue
there so we don't need to do anything to flush the un-commited queue.
What we need to do is to declare the support.

These capabilities are required to pass Windows SVVP test program.  It
is verified that when with parameters "x-aw-bits=48,caching-mode=off"
we can pass the Windows SVVP test with this patch applied.  Otherwise
we'll fail with:

        IOMMU[0] - DWD (DMA write draining) not supported
        IOMMU[0] - DWD (DMA read draining) not supported
        Segment 0 has no DMA remapping capable IOMMU units

However since these bits are not declared support for QEMU<=3.1, we'll
need a compatibility bit for it and we turn this on by default only
for QEMU>=4.0.

Please refer to VT-d spec 6.5.4 for more information.

CC: Yu Wang <wyu@redhat.com>
Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1654550
Signed-off-by: Peter Xu <peterx@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 4806d7edb4..26cc731c7b 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -2659,6 +2659,7 @@ static Property vtd_properties[] = {
     DEFINE_PROP_UINT8("x-aw-bits", IntelIOMMUState, aw_bits,
                       VTD_HOST_ADDRESS_WIDTH),
     DEFINE_PROP_BOOL("caching-mode", IntelIOMMUState, caching_mode, FALSE),
+    DEFINE_PROP_BOOL("dma-drain", IntelIOMMUState, dma_drain, true),
     DEFINE_PROP_END_OF_LIST(),
 };
 
@@ -3147,6 +3148,9 @@ static void vtd_init(IntelIOMMUState *s)
     s->cap = VTD_CAP_FRO | VTD_CAP_NFR | VTD_CAP_ND |
              VTD_CAP_MAMV | VTD_CAP_PSI | VTD_CAP_SLLPS |
              VTD_CAP_SAGAW_39bit | VTD_CAP_MGAW(s->aw_bits);
+    if (s->dma_drain) {
+        s->cap |= VTD_CAP_DRAIN;
+    }
     if (s->aw_bits == VTD_HOST_AW_48BIT) {
         s->cap |= VTD_CAP_SAGAW_48bit;
     }