Each network packet is submitted for transmission by pushing the head
descriptor of a two-part descriptor chain to the Available Ring of the
TX queue. VirtioNetInitTx() sets up the the descriptor chains for all
queueable packets in advance, and points all the head descriptors to the
same shared, never modified, VIRTIO_1_0_NET_REQ header object (or its
initial VIRTIO_NET_REQ sub-object, dependent on virtio version).
VirtioNetInitTx() currently uses the header object's system physical
address for populating the head descriptors.

When device is behind the IOMMU, VirtioNet driver is required to provide
the device address of VIRTIO_1_0_NET_REQ header. In this patch we
dynamically allocate the header using AllocateSharedPages() and map with
BusMasterCommonBuffer so that header can be accessed by both processor
and the device.

We map the header object for CommonBuffer operation because, in order to
stick with the current code order, we populate the head descriptors with
the header's device address first, and fill in the header itself second.

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
---
 OvmfPkg/VirtioNetDxe/VirtioNet.h        |  3 +-
 OvmfPkg/VirtioNetDxe/SnpInitialize.c    | 64 +++++++++++++++++---
 OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c |  7 +++
 3 files changed, 65 insertions(+), 9 deletions(-)

diff --git a/OvmfPkg/VirtioNetDxe/VirtioNet.h b/OvmfPkg/VirtioNetDxe/VirtioNet.h
index 995593f4b236..027f75993e8e 100644
--- a/OvmfPkg/VirtioNetDxe/VirtioNet.h
+++ b/OvmfPkg/VirtioNetDxe/VirtioNet.h
@@ -97,7 +97,8 @@ typedef struct {
   UINT16                      TxMaxPending;      // VirtioNetInitTx
   UINT16                      TxCurPending;      // VirtioNetInitTx
   UINT16                      *TxFreeStack;      // VirtioNetInitTx
-  VIRTIO_1_0_NET_REQ          TxSharedReq;       // VirtioNetInitTx
+  VIRTIO_1_0_NET_REQ          *TxSharedReq;      // VirtioNetInitTx
+  VOID                        *TxSharedReqMap;   // VirtioNetInitTx
   UINT16                      TxLastUsed;        // VirtioNetInitTx
 } VNET_DEV;
 
diff --git a/OvmfPkg/VirtioNetDxe/SnpInitialize.c b/OvmfPkg/VirtioNetDxe/SnpInitialize.c
index b739875d4c01..9621f936d2cb 100644
--- a/OvmfPkg/VirtioNetDxe/SnpInitialize.c
+++ b/OvmfPkg/VirtioNetDxe/SnpInitialize.c
@@ -18,6 +18,7 @@
 **/
 
 #include <Library/BaseLib.h>
+#include <Library/BaseMemoryLib.h>
 #include <Library/MemoryAllocationLib.h>
 #include <Library/UefiBootServicesTableLib.h>
 
@@ -147,6 +148,9 @@ ReleaseQueue:
 
   @retval EFI_OUT_OF_RESOURCES  Failed to allocate the stack to track the heads
                                 of free descriptor chains.
+  @return                       Status codes from VIRTIO_DEVICE_PROTOCOL.
+                                AllocateSharedPages() or
+                                VirtioMapAllBytesInSharedBuffer()
   @retval EFI_SUCCESS           TX setup successful.
 */
 
@@ -157,8 +161,11 @@ VirtioNetInitTx (
   IN OUT VNET_DEV *Dev
   )
 {
-  UINTN TxSharedReqSize;
-  UINTN PktIdx;
+  UINTN                 TxSharedReqSize;
+  UINTN                 PktIdx;
+  EFI_STATUS            Status;
+  EFI_PHYSICAL_ADDRESS  DeviceAddress;
+  VOID                  *TxSharedReqBuffer;
 
   Dev->TxMaxPending = (UINT16) MIN (Dev->TxRing.QueueSize / 2,
                                  VNET_MAX_PENDING);
@@ -170,12 +177,42 @@ VirtioNetInitTx (
   }
 
   //
+  // Allocate TxSharedReq header and map with BusMasterCommonBuffer so that it
+  // can be accessed equally by both processor and device.
+  //
+  Status = Dev->VirtIo->AllocateSharedPages (
+                          Dev->VirtIo,
+                          EFI_SIZE_TO_PAGES (sizeof *Dev->TxSharedReq),
+                          &TxSharedReqBuffer
+                          );
+  if (EFI_ERROR (Status)) {
+    goto FreeTxFreeStack;
+  }
+
+  ZeroMem (TxSharedReqBuffer, sizeof *Dev->TxSharedReq);
+
+  Status = VirtioMapAllBytesInSharedBuffer (
+             Dev->VirtIo,
+             VirtioOperationBusMasterCommonBuffer,
+             TxSharedReqBuffer,
+             sizeof *(Dev->TxSharedReq),
+             &DeviceAddress,
+             &Dev->TxSharedReqMap
+             );
+  if (EFI_ERROR (Status)) {
+    goto FreeTxSharedReqBuffer;
+  }
+
+  Dev->TxSharedReq = TxSharedReqBuffer;
+
+
+  //
   // In VirtIo 1.0, the NumBuffers field is mandatory. In 0.9.5, it depends on
   // VIRTIO_NET_F_MRG_RXBUF, which we never negotiate.
   //
   TxSharedReqSize = (Dev->VirtIo->Revision < VIRTIO_SPEC_REVISION (1, 0, 0)) ?
-                    sizeof Dev->TxSharedReq.V0_9_5 :
-                    sizeof Dev->TxSharedReq;
+                    sizeof (Dev->TxSharedReq->V0_9_5) :
+                    sizeof *Dev->TxSharedReq;
 
   for (PktIdx = 0; PktIdx < Dev->TxMaxPending; ++PktIdx) {
     UINT16 DescIdx;
@@ -187,7 +224,7 @@ VirtioNetInitTx (
     // For each possibly pending packet, lay out the descriptor for the common
     // (unmodified by the host) virtio-net request header.
     //
-    Dev->TxRing.Desc[DescIdx].Addr  = (UINTN) &Dev->TxSharedReq;
+    Dev->TxRing.Desc[DescIdx].Addr  = DeviceAddress;
     Dev->TxRing.Desc[DescIdx].Len   = (UINT32) TxSharedReqSize;
     Dev->TxRing.Desc[DescIdx].Flags = VRING_DESC_F_NEXT;
     Dev->TxRing.Desc[DescIdx].Next  = (UINT16) (DescIdx + 1);
@@ -202,13 +239,13 @@ VirtioNetInitTx (
   //
   // virtio-0.9.5, Appendix C, Packet Transmission
   //
-  Dev->TxSharedReq.V0_9_5.Flags   = 0;
-  Dev->TxSharedReq.V0_9_5.GsoType = VIRTIO_NET_HDR_GSO_NONE;
+  Dev->TxSharedReq->V0_9_5.Flags   = 0;
+  Dev->TxSharedReq->V0_9_5.GsoType = VIRTIO_NET_HDR_GSO_NONE;
 
   //
   // For VirtIo 1.0 only -- the field exists, but it is unused
   //
-  Dev->TxSharedReq.NumBuffers = 0;
+  Dev->TxSharedReq->NumBuffers = 0;
 
   //
   // virtio-0.9.5, 2.4.2 Receiving Used Buffers From the Device
@@ -223,6 +260,17 @@ VirtioNetInitTx (
   *Dev->TxRing.Avail.Flags = (UINT16) VRING_AVAIL_F_NO_INTERRUPT;
 
   return EFI_SUCCESS;
+
+FreeTxSharedReqBuffer:
+  Dev->VirtIo->FreeSharedPages (
+                 Dev->VirtIo,
+                 EFI_SIZE_TO_PAGES (sizeof *(Dev->TxSharedReq)),
+                 TxSharedReqBuffer
+                 );
+FreeTxFreeStack:
+  FreePool (Dev->TxFreeStack);
+
+  return Status;
 }
 
 
diff --git a/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c b/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c
index ee4f9ed36ecd..2fce8142d554 100644
--- a/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c
+++ b/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c
@@ -54,6 +54,13 @@ VirtioNetShutdownTx (
   IN OUT VNET_DEV *Dev
   )
 {
+  Dev->VirtIo->UnmapSharedBuffer (Dev->VirtIo, Dev->TxSharedReqMap);
+  Dev->VirtIo->FreeSharedPages (
+                 Dev->VirtIo,
+                 EFI_SIZE_TO_PAGES (sizeof *(Dev->TxSharedReq)),
+                 Dev->TxSharedReq
+                 );
+
   FreePool (Dev->TxFreeStack);
 }
 
-- 
2.9.5

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