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Message-ID: <Y7c3mQS1zqw0UATF@google.com>
Date: Thu, 5 Jan 2023 20:48:25 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Akihiko Odaki <akihiko.odaki@...nix.com>
Cc: Mark Brown <broonie@...nel.org>, Marc Zyngier <maz@...nel.org>,
linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev,
kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
Mathieu Poirier <mathieu.poirier@...aro.org>,
Suzuki K Poulose <suzuki.poulose@....com>,
Alexandru Elisei <alexandru.elisei@....com>,
James Morse <james.morse@....com>,
Will Deacon <will@...nel.org>,
Catalin Marinas <catalin.marinas@....com>,
asahi@...ts.linux.dev, Alyssa Rosenzweig <alyssa@...enzweig.io>,
Sven Peter <sven@...npeter.dev>,
Hector Martin <marcan@...can.st>
Subject: Re: [PATCH v4 6/7] KVM: arm64: Mask FEAT_CCIDX
Hi Akihiko,
On Thu, Dec 22, 2022 at 05:40:15AM +0900, Akihiko Odaki wrote:
> The CCSIDR access handler masks the associativity bits according to the
> bit layout for processors without FEAT_CCIDX. KVM also assumes CCSIDR is
> 32-bit where it will be 64-bit if FEAT_CCIDX is enabled. Mask FEAT_CCIDX
> so that these assumptions hold.
>
> Suggested-by: Marc Zyngier <maz@...nel.org>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@...nix.com>
> ---
> arch/arm64/kvm/sys_regs.c | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index f4a7c5abcbca..aeabf1f3370b 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -1124,6 +1124,12 @@ static u64 read_id_reg(const struct kvm_vcpu *vcpu, struct sys_reg_desc const *r
> ID_DFR0_PERFMON_SHIFT,
> kvm_vcpu_has_pmu(vcpu) ? ID_DFR0_PERFMON_8_4 : 0);
> break;
> + case SYS_ID_AA64MMFR2_EL1:
> + val &= ~ID_AA64MMFR2_EL1_CCIDX_MASK;
> + break;
> + case SYS_ID_MMFR4_EL1:
> + val &= ~ARM64_FEATURE_MASK(ID_MMFR4_CCIDX);
> + break;
Not that it is necessarily worth addressing, but I wanted to point
something out.
This change breaks migration from older kernels on implementations w/
FEAT_CCIDX. There is most likely exactly 0 of those in the wild, but
we need to be careful changing user-visible stuff like this.
--
Thanks,
Oliver
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