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

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

On Fri, Mar 16, 2018 at 11:28:21AM +0000, Ard Biesheuvel wrote:
> On 15 March 2018 at 19:01, Leif Lindholm <leif.lindholm@linaro.org> wrote:
> > 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?
> 
> It will affects VMs running new firmware on ancient host kernels (and
> v4.2 *is* ancient when it comes to KVM/arm64 and server stuff imo)

Oh, it is, but if we have
https://bugs.launchpad.net/ubuntu/+source/edk2/+bug/1744754
(Xenial guest), imagining people running a Zesty host isn't that much
more of a stretch (it's only EOL 2 months ago).

/
    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
> >>