Thanks Lazlo, I had this issue with the ARM FVP Models and its Virtio support (see: http://infocenter.arm.com/help/topic/com.arm.doc.dui0834a/Chunk446462681.html). I do not remember which model version. I am happy to abandon this patch until I track down the model version and an action is taken by the ARM model team to fix it.
-----Original Message----- From: Laszlo Ersek [mailto:ler...@redhat.com] Sent: 09 July 2015 18:30 To: Olivier Martin Cc: jordan.l.jus...@intel.com; edk2-devel@lists.sourceforge.net Subject: Re: [PATCH] OvmfPkg/VirtioLib: Ensure VirtioFlush() is not blocked On 07/09/15 18:47, Olivier Martin wrote: > .. in case the platform does not received the used buffer from the > device, VirtioFlush() returns EFI_TIMEOUT. > > Contributed-under: TianoCore Contribution Agreement 1.0 > Signed-off-by: Olivier Martin <olivier.mar...@arm.com> > --- > OvmfPkg/Include/Library/VirtioLib.h | 3 +++ > OvmfPkg/Library/VirtioLib/VirtioLib.c | 16 ++++++++++++++-- > 2 files changed, 17 insertions(+), 2 deletions(-) > > diff --git a/OvmfPkg/Include/Library/VirtioLib.h > b/OvmfPkg/Include/Library/VirtioLib.h > index 36527a5..62f6811 100644 > --- a/OvmfPkg/Include/Library/VirtioLib.h > +++ b/OvmfPkg/Include/Library/VirtioLib.h > @@ -170,6 +170,9 @@ VirtioAppendDesc ( > > @return Error code from VirtIo->SetQueueNotify() if it fails. > > + @retval EFI_TIMEOUT If it did not received the used buffer from the device > + in approximatively less than 10ms > + > @retval EFI_SUCCESS Otherwise, the host processed all descriptors. > > **/ > diff --git a/OvmfPkg/Library/VirtioLib/VirtioLib.c > b/OvmfPkg/Library/VirtioLib/VirtioLib.c > index 54cf225..566f596 100644 > --- a/OvmfPkg/Library/VirtioLib/VirtioLib.c > +++ b/OvmfPkg/Library/VirtioLib/VirtioLib.c > @@ -3,7 +3,7 @@ > Utility functions used by virtio device drivers. > > Copyright (C) 2012, Red Hat, Inc. > - Portion of Copyright (C) 2013, ARM Ltd. > + Portion of Copyright (C) 2013-2014, ARM Ltd. > > This program and the accompanying materials are licensed and made available > under the terms and conditions of the BSD License which accompanies > this @@ -252,6 +252,9 @@ VirtioAppendDesc ( > > @return Error code from VirtIo->SetQueueNotify() if it fails. > > + @retval EFI_TIMEOUT If it did not received the used buffer from the device > + in approximatively less than 10ms > + > @retval EFI_SUCCESS Otherwise, the host processed all descriptors. > > **/ > @@ -267,6 +270,7 @@ VirtioFlush ( > UINT16 NextAvailIdx; > EFI_STATUS Status; > UINTN PollPeriodUsecs; > + UINTN Timeout; > > // > // virtio-0.9.5, 2.4.1.2 Updating the Available Ring @@ -304,16 > +308,24 @@ VirtioFlush ( > // Keep slowing down until we reach a poll period of slightly above 1 ms. > // > PollPeriodUsecs = 1; > + Timeout = 0; > MemoryFence(); > - while (*Ring->Used.Idx != NextAvailIdx) { > + while ((*Ring->Used.Idx != NextAvailIdx) && (Timeout < 10)) { > gBS->Stall (PollPeriodUsecs); // calls > AcpiTimerLib::MicroSecondDelay > > if (PollPeriodUsecs < 1024) { > PollPeriodUsecs *= 2; > + } else { > + Timeout++; > } > MemoryFence(); > } > > MemoryFence(); > + > + if (Timeout == 10) { > + return EFI_TIMEOUT; > + } > + > return EFI_SUCCESS; > } > I think if this ever happens, that's a bug in the host / hypervisor. Under what conditions are you seeing this as necessary? VirtioFlush() blocks infinitely on purpose in this loop. The protocol does not define any circumstances for timeout. The communicating peers are not connected by a fragile network link, they are connected by host memory. Whenever you time out, that's an arbitrary decision; it might even misfire dependent on host load. If you think this is really necessary, then please introduce an integer PCD. The default value of the PCD (probably 0) should preserve existing behavior. The PCD should be then overridden by downstreams (by directly editing the appropriate DSC file). Alternatively, if you have a specific host platform in mind that necessitates this change (and for which the value 10 also seems right), then please introduce a new build flag as well (in the affected DSC(s)). People who build for that platform can then hardcode that flag in their build scripts. There are two users of VirtioFlush(): the virtio-blk and virtio-scsi drivers. Both check for (and propagate) any errors returned by VirtioFlush() correctly. Any timeout error would reach the outermost callers (the respective protocol users) just fine. So those parts of the tree need not be fixed up, I agree. Still, this patch would work around a host bug, as far as I understand, and the actual timeout looks arbitrary, so it should be off by default, and controllable without modifying the C source. The commit message (and the PCD's comment) should also identify the host platform that requires this as precisely as possible. ... Obviously, it is *also* possible that the guest code has some other bug, elsewhere. (We can never exclude that, unless we prove the code correct with formal tools.) It seems quite unlikely, but if that's the case, then I'd prefer to track it down and fix it, instead of papering it over. Thanks! 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