linux-kernel - Re: [PATCH 1/1] KVM: arm/arm64: arch_timer: Fix TimerValue TVAL calculation in KVM

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Message-ID: <86wokg65z5.wl-marc.zyngier@arm.com>
Date:   Sat, 30 Mar 2019 09:56:14 +0000
From:   Marc Zyngier <marc.zyngier@....com>
To:     Wei Huang <wei@...hat.com>
Cc:     <linux-kernel@...r.kernel.org>, <kvmarm@...ts.cs.columbia.edu>,
        <linux-arm-kernel@...ts.infradead.org>, <andre.przywara@....com>,
        <christoffer.dall@....com>, <james.morse@....com>,
        <julien.thierry@....com>, <suzuki.poulose@....com>
Subject: Re: [PATCH 1/1] KVM: arm/arm64: arch_timer: Fix TimerValue TVAL calculation in KVM

On Fri, 29 Mar 2019 20:12:53 +0000,
Wei Huang <wei@...hat.com> wrote:
> 
> Recently the generic timer test of kvm-unit-tests failed to complete
> (stalled) when a physical timer is being used. This issue is caused
> by incorrect update of CNT_CVAL when TimerValue is being accessed,
> introduced by 'Commit 84135d3d18da ("KVM: arm/arm64: consolidate arch
> timer trap handlers")'. According to Arm ARM, the read/write behavior
> of accesses to TimeValue registers is expected to be:
> 
>   * READ: TimerValue = (CompareValue – (Counter - Offset)
>   * WRITE: CompareValue = ((Counter - Offset) + Sign(TimerValue)
> 
> This patch fixes the TVAL read/write code path according to the
> specification.
> 
> Signed-off-by: Wei Huang <wei@...hat.com>

Huh... Nice catch. I guess I only ran this with a VHE host, where this
code path is unused.

Thanks,

	M.

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