From: Marc Zyngier <maz@kernel•org>
To: Mark Brown <broonie@kernel•org>
Cc: Oliver Upton <oupton@kernel•org>, Joey Gouly <joey.gouly@arm•com>,
Steffen Eiden <seiden@linux•ibm.com>,
Suzuki K Poulose <suzuki.poulose@arm•com>,
Catalin Marinas <catalin.marinas@arm•com>,
Will Deacon <will@kernel•org>,
Mark Rutland <mark.rutland@arm•com>,
linux-arm-kernel@lists•infradead.org, kvmarm@lists•linux.dev,
linux-kernel@vger•kernel.org
Subject: Re: [PATCH] KVM: arm64: Preserve all guest ZCR_EL2.LEN values
Date: Sat, 23 May 2026 16:24:52 +0100 [thread overview]
Message-ID: <87fr3i9mij.wl-maz@kernel.org> (raw)
In-Reply-To: <ahG75BY6yvaePj-B@sirena.org.uk>
On Sat, 23 May 2026 15:38:28 +0100,
Mark Brown <broonie@kernel•org> wrote:
>
> On Sat, May 23, 2026 at 09:47:38AM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel•org> wrote:
>
> > > Currently all other bits in ZCR_EL2 are either RES0 or RAZ/WI, values
> > > written are sanitised based on this.
>
> > Only for the direct writes to ZCR_EL2, as they are trapping. I don't
> > see any sanitisation for writes using the ZCR_EL1 accessor, which is
> > the common case. This needs fixing at the same time.
>
> OK, I'll convert ZCR_EL2 to a sanitised register. As I mentioned I was
> a bit confused about why the existing code is the way it is and so
> followed it in only managing the direct writes. I figured it was
> considered OK to rely on the hardware for the RES0 and WI behaviour for
> untrapped access.
In general, that's OK. But given that you need sanitisation in the
trapping case, it is way better to have a uniform behaviour and keep
sanitisation at the accessor level. It is also more sustainable in the
long run, should ZCR_ELx get new significant bits.
Thanks,
M.
--
Jazz isn't dead. It just smells funny.
next prev parent reply other threads:[~2026-05-23 15:21 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-22 18:00 [PATCH] KVM: arm64: Preserve all guest ZCR_EL2.LEN values Mark Brown
2026-05-23 8:47 ` Marc Zyngier
2026-05-23 14:38 ` Mark Brown
2026-05-23 15:24 ` Marc Zyngier [this message]
2026-05-25 18:36 ` Mark Rutland
2026-05-26 10:19 ` Mark Brown
2026-05-26 12:03 ` Mark Rutland
2026-05-26 13:03 ` Mark Brown
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