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OvmfPkg: Virtio: load used ring element strictly after loading used index 

Enforce in-order execution of these steps even on not sequentially
consistent architectures, as discussed in [1]. These changes should be
unnecessary on x86 (the only architecture OVMF currently supports), but
they align the OVMF virtio code with the virtio specification and could be
necessary for future OVMF ports.

[1] http://lists.linuxfoundation.org/pipermail/virtualization/2013-June/024547.html

Suggested-by: Stefan Hajnoczi <stefanha@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@14601 6f19259b-4bc3-4df7-8a09-765794883524
This commit is contained in:
Laszlo Ersek 2013-08-23 18:46:03 +00:00 committed by jljusten
parent 9bef3cdc8a
commit dc9447bd37
4 changed files with 4 additions and 0 deletions
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1
OvmfPkg/Library/VirtioLib/VirtioLib.c
View File

@ -456,5 +456,6 @@ VirtioFlush (
MemoryFence();
}
MemoryFence();
return EFI_SUCCESS;
}

1
OvmfPkg/VirtioNetDxe/Events.c
View File

@ -61,6 +61,7 @@ VirtioNetIsPacketAvailable (
//
MemoryFence ();
RxCurUsed = *Dev->RxRing.Used.Idx;
MemoryFence ();
if (Dev->RxLastUsed != RxCurUsed) {
gBS->SignalEvent (&Dev->Snp.WaitForPacket);

1
OvmfPkg/VirtioNetDxe/SnpGetStatus.c
View File

@ -103,6 +103,7 @@ VirtioNetGetStatus (
MemoryFence ();
RxCurUsed = *Dev->RxRing.Used.Idx;
TxCurUsed = *Dev->TxRing.Used.Idx;
MemoryFence ();
if (InterruptStatus != NULL) {
//

1
OvmfPkg/VirtioNetDxe/SnpReceive.c
View File

@ -105,6 +105,7 @@ VirtioNetReceive (
//
MemoryFence ();
RxCurUsed = *Dev->RxRing.Used.Idx;
MemoryFence ();
if (Dev->RxLastUsed == RxCurUsed) {
Status = EFI_NOT_READY;