On 07/10/15 17:22, Olivier Martin wrote: > 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.
I agree that this would be the best course of action -- in November 2013 or so I reported a virtio bug for the Foundation model (case #566785, "full device reset doesn't reset QueuePFNs"), with a reproducer guest kernel: http://people.redhat.com/~lersek/arm_case566785_queuepfn_repro/ The model team at ARM fixed the bug for the next release. It was a positive experience for me. Thanks! Laszlo > > -----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! > Laszlo > > > -- IMPORTANT NOTICE: The contents of this email and any attachments are > confidential and may also be privileged. If you are not the intended > recipient, please notify the sender immediately and do not disclose the > contents to any other person, use it for any purpose, or store or copy the > information in any medium. Thank you. > > ARM Limited, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, > Registered in England & Wales, Company No: 2557590 > ARM Holdings plc, Registered office 110 Fulbourn Road, Cambridge CB1 9NJ, > Registered in England & Wales, Company No: 2548782 > ------------------------------------------------------------------------------ Don't Limit Your Business. Reach for the Cloud. 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