linux-kernel - Re: [PATCH RFC v3 09/27] KVM: arm64: Factor SVE guest exit handling out into a function

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Message-ID: <Z5Dc-WMu2azhTuMn@J2N7QTR9R3>
Date: Wed, 22 Jan 2025 11:56:41 +0000
From: Mark Rutland <mark.rutland@....com>
To: Marc Zyngier <maz@...nel.org>
Cc: Mark Brown <broonie@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Joey Gouly <joey.gouly@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Suzuki K Poulose <suzuki.poulose@....com>,
	Will Deacon <will@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
	Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>,
	Dave Martin <Dave.Martin@....com>, Fuad Tabba <tabba@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC v3 09/27] KVM: arm64: Factor SVE guest exit handling
 out into a function

On Wed, Jan 22, 2025 at 11:51:00AM +0000, Marc Zyngier wrote:
> On Fri, 17 Jan 2025 11:34:09 +0000, Mark Rutland <mark.rutland@....com> wrote:
> > The TL;DR summary is that it's not sufficient for kvm_arch_vcpu_put_fp()
> > to fix up ZCR_ELx. Either:
> > 
> > * That needs to be fixed up while IRQs are masked, e.g. by
> >   saving/restoring the host and guest ZCR_EL1 and/or ZCR_ELx values in
> >   kvm_arch_vcpu_ctxflush_fp() and kvm_arch_vcpu_ctxsync_fp()
> > 
> > * The lazy save logic in fpsimd_save_user_state() needs to handle KVM
> >   explicitly, saving the guest's ZCR_EL1 and restoring the host's
> >   ZCR_ELx.
> > 
> > I think we need to fix that before we extend this logic for SME.
> 
> So save/restore ZCR_ELx eagerly? If that's what it takes, let's do
> that now.

I believe that's sufficient; I'll go double-check and spin that now.

Mark.