Re: [PATCH v2] ArmPkg/TimerDxe: remove workaround for KVM timer handling

[Julien Grall <julien.grall@arm.com>]

Hi Ard,

Sorry for the late reply.

On 19/04/18 09:16, Ard Biesheuvel wrote:
> On 17 April 2018 at 08:03, Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>> When we first ported EDK2 to KVM/arm, we implemented a workaround for
>> the quirky timer handling on the KVM side. This has been fixed in
>> Linux commit f120cd6533d2 ("KVM: arm/arm64: timer: Allow the timer to
>> control the active state") dated 23 June 2014, which was incorporated
>> into Linux release 4.3.
>>
>> So almost 4 years later, it should be safe to drop this workaround on
>> the EDK2 side.
>>
>> This reverts commit b1a633434ddc.
>>
>> Cc: cross-distro@lists.linaro.org
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>> Acked-by: Marc Zyngier <marc.zyngier@arm.com>
>> Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
>> Acked-by: Laszlo Ersek <lersek@redhat.com>
> 
> Pushed as 411a373ed6426fb1bff253905b6a59ada44e18ad

While this was added for KVM, I believe that code is also needed by Xen. 
Indeed before injecting the interrupt the hypervisor will mask the 
interrupt.

So would it be possible to revert that patch?

Cheers,

> 
> Thanks all
> 
>> ---
>> v2: add acks
>>
>> Note to cross-distro readers: this means guest firmware built with this patch
>> will not work on KVM/ARM hosts using kernel v4.2 or earlier.
>>
>>   ArmPkg/Drivers/TimerDxe/TimerDxe.c                                           |  1 -
>>   ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c | 10 ----------
>>   2 files changed, 11 deletions(-)
>>
>> diff --git a/ArmPkg/Drivers/TimerDxe/TimerDxe.c b/ArmPkg/Drivers/TimerDxe/TimerDxe.c
>> index a3202fa056f3..bd616d2efc73 100644
>> --- a/ArmPkg/Drivers/TimerDxe/TimerDxe.c
>> +++ b/ArmPkg/Drivers/TimerDxe/TimerDxe.c
>> @@ -337,7 +337,6 @@ TimerInterruptHandler (
>>
>>       // Set next compare value
>>       ArmGenericTimerSetCompareVal (CompareValue);
>> -    ArmGenericTimerEnableTimer ();
>>       ArmInstructionSynchronizationBarrier ();
>>     }
>>
>> diff --git a/ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c b/ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c
>> index 69a4ceb62db6..c941895a3574 100644
>> --- a/ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c
>> +++ b/ArmPkg/Library/ArmGenericTimerVirtCounterLib/ArmGenericTimerVirtCounterLib.c
>> @@ -26,16 +26,6 @@ ArmGenericTimerEnableTimer (
>>
>>     TimerCtrlReg = ArmReadCntvCtl ();
>>     TimerCtrlReg |= ARM_ARCH_TIMER_ENABLE;
>> -
>> -  //
>> -  // When running under KVM, we need to unmask the interrupt on the timer side
>> -  // as KVM will mask it when servicing the interrupt at the hypervisor level
>> -  // and delivering the virtual timer interrupt to the guest. Otherwise, the
>> -  // interrupt will fire again, trapping into the hypervisor again, etc. etc.
>> -  // This is scheduled to be fixed on the KVM side, but there is no harm in
>> -  // leaving this in once KVM gets fixed.
>> -  //
>> -  TimerCtrlReg &= ~ARM_ARCH_TIMER_IMASK;
>>     ArmWriteCntvCtl (TimerCtrlReg);
>>   }
>>
>> --
>> 2.17.0
>>
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-- 
Julien Grall