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From:   Oliver Upton <oliver.upton@linux.dev>
To:     James Clark <james.clark@arm.com>
Cc:     linux-arm-kernel@lists.infradead.org,
        linux-perf-users@vger.kernel.org, suzuki.poulose@arm.com,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
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        Russell King <linux@armlinux.org.uk>,
        Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Zaid Al-Bassam <zalbassam@google.com>,
        Reiji Watanabe <reijiw@google.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        kvmarm@lists.linux.dev
Subject: Re: [PATCH v3 1/3] arm: perf: Include threshold control fields valid
 in PMEVTYPER mask
Message-ID: <ZSZb2H8O5fuU3UrA@linux.dev>
References: <20231010141551.2262059-1-james.clark@arm.com>
 <20231010141551.2262059-2-james.clark@arm.com>
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Hi James,

On Tue, Oct 10, 2023 at 03:15:41PM +0100, James Clark wrote:
> FEAT_PMUv3_TH (Armv8.8) adds two new fields to PMEVTYPER, so include
> them in the mask. These aren't writable on 32 bit kernels as they are in
> the high part of the register, so split the mask definition to the asm
> files for each platform.
> 
> Now where the value is used in some parts of KVM, include the asm file.
> There is no impact on guest PMUs emulated with KVM because the new
> fields are ignored when constructing the attributes for opening the
> event. But if threshold support is added to KVM at a later time no
> change to the mask will be needed.

KVM should treat TH and TC as RES0 if the feature isn't virtualized. I'd
rather move KVM away from using ARMV8_PMU_EVTYPE_MASK in the first
place. Looks like we already have an issue with the NSH bit, so I've
sent the below patch to fix it.

https://lore.kernel.org/kvmarm/20231011081649.3226792-3-oliver.upton@linux.dev/

-- 
Thanks,
Oliver