Re: [PATCH v3 00/11] KVM: arm64: Fix handling of host fpsimd/sve state in protected mode

From: Oliver Upton <oliver.upton@linux.dev>
To: Fuad Tabba <tabba@google.com>
Cc: kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org,
	maz@kernel.org, will@kernel.org, qperret@google.com,
	seanjc@google.com, alexandru.elisei@arm.com,
	catalin.marinas@arm.com, philmd@linaro.org, james.morse@arm.com,
	suzuki.poulose@arm.com, mark.rutland@arm.com, broonie@kernel.org,
	joey.gouly@arm.com, rananta@google.com, yuzenghui@huawei.com
Subject: Re: [PATCH v3 00/11] KVM: arm64: Fix handling of host fpsimd/sve state in protected mode
Date: Thu, 30 May 2024 11:29:00 -0700	[thread overview]
Message-ID: <ZljFbNcVgYb5Q7KH@linux.dev> (raw)
In-Reply-To: <20240528125914.277057-1-tabba@google.com>

On Tue, May 28, 2024 at 01:59:03PM +0100, Fuad Tabba wrote:
> Changes since v2 [1]
> - Rebased on Linux 6.10-rc1 (1613e604df0c)
> - Apply suggestions/fixes suggested for V2 (Marc)
> - Add an isb() to __hyp_sve_restore_guest()
> - Squash patch that introduces kvm_host_sve_max_vl with following
>   patch, since it's used there
> - Some refactoring and tidying up
> - Introduce and use sve_cond_update_zcr_vq_isb(), which only does
>   an isb() if ZCR is updated (RFC, next to last patch)
> - Remove sve_cond_update_zcr_vq_*, since it's not likely to help
>   much (RFC, last patch)
> 
> With the KVM host data rework [2], handling of fpsimd and sve
> state in protected mode is done at hyp. For protected VMs, we
> don't want to leak any guest state to the host, including whether
> a guest has used fpsimd/sve.
> 
> To complete the work started with the host data rework, in
> regards to protected mode, ensure that the host's fpsimd context
> and its sve context are restored on guest exit, since the rework
> has hidden the fpsimd/sve state from the host.
> 
> This patch series eagerly restores the host fpsimd/sve state on
> guest exit when running in protected mode, which happens only if
> the guest has used fpsimd/sve. This means that the saving of the
> state is lazy, similar to the behavior of KVM in other modes, but
> the restoration of the host state is eager.
> 
> The last two patches are not essential to this patch series, and
> the last one undoes the next-to-last. Please consider only one
> (or neither) of these two patches for inclusion.

For patches 1-7 (with the unnecessary isb()'s addressed):

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>

I think we can do without the rest of the series for 6.10.

I also tested this on Neoverse V2.

-- 
Thanks,
Oliver

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel