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

[Leif Lindholm <leif.lindholm@linaro.org>]

On Thu, Mar 15, 2018 at 10:28:26AM +0000, Ard Biesheuvel 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.
> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>

I'm happy with this, with Marc's Ack.
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>

However, if this can affect old kernels running in vms, could you ping
cross-distro@lists.linaro.org as well, so it doesn't catch anyone by
surprise?

/
    Leif

> ---
>  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);
>  }
>  
> -- 
> 2.15.1
>