linux-kernel - Re: [PATCH 3/3] KVM: arm64: Skip break phase when we have FEAT

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Message-ID: <ZIM+ZgFji/H3Y/9U@linux.dev>
Date:   Fri, 9 Jun 2023 14:59:50 +0000
From:   Oliver Upton <oliver.upton@...ux.dev>
To:     Will Deacon <will@...nel.org>
Cc:     Marc Zyngier <maz@...nel.org>,
        Colton Lewis <coltonlewis@...gle.com>, kvm@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.linux.dev
Subject: Re: [PATCH 3/3] KVM: arm64: Skip break phase when we have FEAT_BBM
 level 2

Hey Will,

On Thu, Jun 08, 2023 at 06:21:13PM +0100, Will Deacon wrote:
> > IIRC, Colton was testing largely with permission relaxation, and had
> > forward progress issues b.c. the stale TLB entry was never invalidated
> > in response to a permission fault.
> 
> Would the series at:
> 
> https://lore.kernel.org/r/5d8e1f752051173d2d1b5c3e14b54eb3506ed3ef.1684892404.git-series.apopple@nvidia.com
> 
> help with that?

Heh, that's a rather interesting patch :)

I don't think it is directly related to the problem Colton encounters,
though the symptoms are similar. This crops up when KVM uses a stricter
permission set than the primary MMU, like lazy X for deferred I$
maintenance and write-protection for dirty logging. KVM policy led to
the stale TLB entry, so KVM is the one that needs to initiate the
invalidation.

-- 
Thanks,
Oliver