linux-kernel - Re: [PATCH 8/9] KVM: arm64: Allow control of dpISA extensions in ID_AA64ISAR3

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Message-ID: <867c9q3lkj.wl-maz@kernel.org>
Date: Tue, 29 Oct 2024 16:45:00 +0000
From: Marc Zyngier <maz@...nel.org>
To: Mark Brown <broonie@...nel.org>
Cc: Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Shuah Khan <shuah@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org,
	kvmarm@...ts.linux.dev,
	linux-kselftest@...r.kernel.org
Subject: Re: [PATCH 8/9] KVM: arm64: Allow control of dpISA extensions in ID_AA64ISAR3_EL1

On Mon, 28 Oct 2024 20:24:17 +0000,
Mark Brown <broonie@...nel.org> wrote:
> 
> ID_AA64ISAR3_EL1 is currently marked as unallocated in KVM but does have a
> number of bitfields defined in it. Expose FPRCVT and FAMINMAX, two simple
> instruction only extensions to guests.
> 
> Signed-off-by: Mark Brown <broonie@...nel.org>
> ---
>  arch/arm64/kvm/sys_regs.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index dad88e31f9537fe02e28b117d6a740f15572e0ba..ab348c314d7963437e1876d441169f3ef4eff095 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -2409,7 +2409,8 @@ static const struct sys_reg_desc sys_reg_descs[] = {
>  	ID_WRITABLE(ID_AA64ISAR2_EL1, ~(ID_AA64ISAR2_EL1_RES0 |
>  					ID_AA64ISAR2_EL1_APA3 |
>  					ID_AA64ISAR2_EL1_GPA3)),
> -	ID_UNALLOCATED(6,3),
> +	ID_WRITABLE(ID_AA64ISAR3_EL1, (ID_AA64ISAR3_EL1_FPRCVT |
> +				       ID_AA64ISAR3_EL1_FAMINMAX)),

Please add the required sanitisation of the register so that we do not
get any surprise exposure of unhandled features when someone changes
ftr_id_aa64isar3[].

	M.

-- 
Without deviation from the norm, progress is not possible.