In one of the following patches, we'll change OvmfPkg/IoMmuDxe so that it
unmaps all existent bus master operations (CommonBuffer, Read, Write) at
ExitBootServices(), strictly after the individual device drivers abort
pending DMA on the devices they manage, in their own ExitBootServices()
notification functions.

In preparation, remove the explicit
VIRTIO_DEVICE_PROTOCOL.UnmapSharedBuffer() call from VirtioScsiExitBoot(),
originally added in commit fc2168feb248 ("OvmfPkg/VirtioScsiDxe: map VRING
using VirtioRingMap()", 2017-08-31).

Add a DEBUG message so we can observe the ordering between
VirtioScsiExitBoot() and the upcoming cleanup of mappings in
OvmfPkg/IoMmuDxe.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Brijesh Singh <brijesh.singh@amd.com>
Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/VirtioScsiDxe/VirtioScsi.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/OvmfPkg/VirtioScsiDxe/VirtioScsi.c b/OvmfPkg/VirtioScsiDxe/VirtioScsi.c
index 7b8c3d22c8de..1a68f062106c 100644
--- a/OvmfPkg/VirtioScsiDxe/VirtioScsi.c
+++ b/OvmfPkg/VirtioScsiDxe/VirtioScsi.c
@@ -1221,25 +1221,20 @@ VirtioScsiExitBoot (
   IN  VOID      *Context
   )
 {
   VSCSI_DEV *Dev;
 
+  DEBUG ((DEBUG_VERBOSE, "%a: Context=0x%p\n", __FUNCTION__, Context));
   //
   // Reset the device. This causes the hypervisor to forget about the virtio
   // ring.
   //
   // We allocated said ring in EfiBootServicesData type memory, and code
   // executing after ExitBootServices() is permitted to overwrite it.
   //
   Dev = Context;
   Dev->VirtIo->SetDeviceStatus (Dev->VirtIo, 0);
-
-  //
-  // Unmap the ring buffer so that hypervisor will not be able to get
-  // readable data after device reset.
-  //
-  Dev->VirtIo->UnmapSharedBuffer (Dev->VirtIo, Dev->RingMap);
 }
 
 
 //
 // Probe, start and stop functions of this driver, called by the DXE core for
-- 
2.14.1.3.gb7cf6e02401b


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