A network packets are transmitted by placing then into a transmit queue,
each packet is preceded by a VIRTIO_1_0_NET_REQ header. VirtioNetInitTx(),
builds the header once and fills the vring descriptors with the system
physical address of header.

The patch uses VirtIo->AllocateSharedPages() to allocate the header buffer
and map it with BusMasterCommonBuffer so that it can be equally accessed by
both processor and device.

We could map it with  BusMasterRead but since the header pointer is
used after it was added into vring hence I choose to dynamically allocate
it and map it with BusMasterCommonBuffer to avoid the code complexity.

Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>
Cc: Jordan Justen <jordan.l.jus...@intel.com>
Cc: Tom Lendacky <thomas.lenda...@amd.com>
Cc: Laszlo Ersek <ler...@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Brijesh Singh <brijesh.si...@amd.com>
---
 OvmfPkg/VirtioNetDxe/VirtioNet.h        |  3 +-
 OvmfPkg/VirtioNetDxe/Events.c           |  5 +++
 OvmfPkg/VirtioNetDxe/SnpInitialize.c    | 41 ++++++++++++++++----
 OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c |  9 +++++
 4 files changed, 49 insertions(+), 9 deletions(-)

diff --git a/OvmfPkg/VirtioNetDxe/VirtioNet.h b/OvmfPkg/VirtioNetDxe/VirtioNet.h
index a4661bd5d2fe..873069e9de82 100644
--- a/OvmfPkg/VirtioNetDxe/VirtioNet.h
+++ b/OvmfPkg/VirtioNetDxe/VirtioNet.h
@@ -94,7 +94,8 @@ 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/Events.c b/OvmfPkg/VirtioNetDxe/Events.c
index 171b144518a9..0004898eab6e 100644
--- a/OvmfPkg/VirtioNetDxe/Events.c
+++ b/OvmfPkg/VirtioNetDxe/Events.c
@@ -107,4 +107,9 @@ VirtioNetExitBoot (
     VirtioUnmapSharedBuffer (Dev->VirtIo, Dev->RxBufMap);
     Dev->RxBufMap = NULL;
   }
+
+  if (Dev->TxSharedReqMap != NULL) {
+    VirtioUnmapSharedBuffer (Dev->VirtIo, Dev->TxSharedReqMap);
+    Dev->TxSharedReqMap = NULL;
+  }
 }
diff --git a/OvmfPkg/VirtioNetDxe/SnpInitialize.c 
b/OvmfPkg/VirtioNetDxe/SnpInitialize.c
index 59c9f1ed3516..9df9f7af32cc 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>
 
@@ -139,8 +140,10 @@ VirtioNetInitTx (
   IN OUT VNET_DEV *Dev
   )
 {
-  UINTN TxSharedReqSize;
-  UINTN PktIdx;
+  UINTN       TxSharedReqSize;
+  UINTN       PktIdx;
+  UINTN       NumPages;
+  EFI_STATUS  Status;
 
   Dev->TxMaxPending = (UINT16) MIN (Dev->TxRing.QueueSize / 2,
                                  VNET_MAX_PENDING);
@@ -152,12 +155,34 @@ VirtioNetInitTx (
   }
 
   //
+  // Allocate TxSharedReq header and map with BusMasterCommonBuffer so that it
+  // can be accessed equally by both processor and device.
+  //
+  NumPages = EFI_SIZE_TO_PAGES (sizeof *(Dev->TxSharedReq));
+  Status = VirtioAllocateSharedPages (Dev->VirtIo, NumPages,
+             (VOID *) &Dev->TxSharedReq);
+  if (EFI_ERROR (Status)) {
+    return Status;
+  }
+
+  Status = VirtioMapSharedBufferCommon (Dev->VirtIo,
+             (VOID *) Dev->TxSharedReq, sizeof *(Dev->TxSharedReq),
+             &Dev->TxSharedReqMap);
+  if (EFI_ERROR (Status)) {
+    VirtioFreeSharedPages (Dev->VirtIo, NumPages,
+      (VOID *) Dev->TxSharedReqMap);
+    return Status;
+  }
+
+  ZeroMem ((VOID *) Dev->TxSharedReq, sizeof *(Dev->TxSharedReq));
+
+  //
   // 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;
@@ -169,7 +194,7 @@ 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  = (UINTN) Dev->TxSharedReq;
     Dev->TxRing.Desc[DescIdx].Len   = (UINT32) TxSharedReqSize;
     Dev->TxRing.Desc[DescIdx].Flags = VRING_DESC_F_NEXT;
     Dev->TxRing.Desc[DescIdx].Next  = (UINT16) (DescIdx + 1);
@@ -184,13 +209,13 @@ 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
diff --git a/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c 
b/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c
index 48cd4900911c..3ed7132be531 100644
--- a/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c
+++ b/OvmfPkg/VirtioNetDxe/SnpSharedHelpers.c
@@ -57,5 +57,14 @@ VirtioNetShutdownTx (
   IN OUT VNET_DEV *Dev
   )
 {
+  if (Dev->TxSharedReqMap != NULL) {
+    VirtioUnmapSharedBuffer (Dev->VirtIo, Dev->TxSharedReqMap);
+    Dev->TxSharedReqMap = NULL;
+  }
+
+  VirtioFreeSharedPages (Dev->VirtIo,
+    EFI_SIZE_TO_PAGES (sizeof *(Dev->TxSharedReq)),
+    (VOID *) Dev->TxSharedReq);
+
   FreePool (Dev->TxFreeStack);
 }
-- 
2.7.4

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