linux-kernel - Re: [RFC 3/3] KVM: arm64: pmu: Enforce PMEVTYPER evtCount size

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Date:   Thu, 5 Dec 2019 10:37:24 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Will Deacon <will@...nel.org>
Cc:     eric.auger.pro@...il.com, maz@...nel.org,
        linux-kernel@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        james.morse@....com, andrew.murray@....com, suzuki.poulose@....com,
        drjones@...hat.com
Subject: Re: [RFC 3/3] KVM: arm64: pmu: Enforce PMEVTYPER evtCount size

Hi Will,

On 12/5/19 10:02 AM, Will Deacon wrote:
> On Wed, Dec 04, 2019 at 09:44:26PM +0100, Eric Auger wrote:
>> ARMv8.1-PMU supports 16-bit evtCount whereas 8.0 only supports
>> 10 bits.
>>
>> On Seatlle which has an 8.0 PMU implementation, evtCount[15:10]
>> are not read as 0, as expected. Fix that by applying a mask on
>> the selected event that depends on the PMU version.
> 
> Are you sure about that? These bits are RES0 in 8.0 afaict, so this would be
> a CPU erratum. Have you checked the SDEN document (I haven't)?

You're right. It is RES0 and not RAZ. My mistake. Please ignore this patch.

Thank you for the feedback.

Eric
> 
> Will
>