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

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

[Ard Biesheuvel]

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>
---
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

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

[Ard Biesheuvel]

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

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
>

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

[Julien Grall]

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
>>
> _______________________________________________
> cross-distro mailing list
> cross-distro@lists.linaro.org
> https://lists.linaro.org/mailman/listinfo/cross-distro
> 

-- 
Julien Grall

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

[Ard Biesheuvel]

On 19 April 2018 at 16:23, Julien Grall <julien.grall@arm.com> wrote:
> 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?
>

Given that this is now a Xen-only quirk, I'd rather work around it by
creating a separate ArmGenericTimerCounterLib implementation for Xen.

I will try to put something together beginning of next week.

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

[Julien Grall]

On 19/04/18 15:34, Ard Biesheuvel wrote:
> On 19 April 2018 at 16:23, Julien Grall <julien.grall@arm.com> wrote:
>> 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?
>>
> 
> Given that this is now a Xen-only quirk, I'd rather work around it by
> creating a separate ArmGenericTimerCounterLib implementation for Xen.

That would work for me.

> 
> I will try to put something together beginning of next week.

I am happy to test it.

Cheers,

-- 
Julien Grall