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From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Zhang Lei <zhang.lei@jp.fujitsu.com>,
	Andre Przywara <andre.przywara@arm.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 1/7] KVM: arm64: Discard any SVE state when entering KVM guests
Date: Wed, 21 Sep 2022 18:31:28 +0100	[thread overview]
Message-ID: <87mtask51r.wl-maz@kernel.org> (raw)
In-Reply-To: <YyogzYzVbb3mvZWM@sirena.org.uk>

On Tue, 20 Sep 2022 21:21:33 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> [1  <text/plain; us-ascii (quoted-printable)>]
> On Tue, Sep 20, 2022 at 05:44:01PM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
> 
> > >  void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
> > >  {
> > >  	BUG_ON(!current->mm);
> > > -	BUG_ON(test_thread_flag(TIF_SVE));
> > > +
> > > +	fpsimd_kvm_prepare();
> > 
> > Why is this *before* the check against system_supports_fpsimd()? I
> > don't think the architecture allows SVE without FP, for obvious
> > reasons...
> 
> Good point, though now that I think about it I can't think of a
> requirement for FP when implementing SME (there's certainly not
> one for SVE).

Even if the architecture was allowing this madness, KVM doesn't allow
SVE if FP is not available, just like the rest of the kernel.

> There's no use for that hook now though.

Care to clarify?

	M.

-- 
Without deviation from the norm, progress is not possible.
_______________________________________________
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kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

WARNING: multiple messages have this Message-ID (diff)
From: Marc Zyngier <maz@kernel.org>
To: Mark Brown <broonie@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Zhang Lei <zhang.lei@jp.fujitsu.com>,
	James Morse <james.morse@arm.com>,
	Alexandru Elisei <alexandru.elisei@arm.com>,
	Andre Przywara <andre.przywara@arm.com>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 1/7] KVM: arm64: Discard any SVE state when entering KVM guests
Date: Wed, 21 Sep 2022 18:31:28 +0100	[thread overview]
Message-ID: <87mtask51r.wl-maz@kernel.org> (raw)
In-Reply-To: <YyogzYzVbb3mvZWM@sirena.org.uk>

On Tue, 20 Sep 2022 21:21:33 +0100,
Mark Brown <broonie@kernel.org> wrote:
> 
> [1  <text/plain; us-ascii (quoted-printable)>]
> On Tue, Sep 20, 2022 at 05:44:01PM +0100, Marc Zyngier wrote:
> > Mark Brown <broonie@kernel.org> wrote:
> 
> > >  void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
> > >  {
> > >  	BUG_ON(!current->mm);
> > > -	BUG_ON(test_thread_flag(TIF_SVE));
> > > +
> > > +	fpsimd_kvm_prepare();
> > 
> > Why is this *before* the check against system_supports_fpsimd()? I
> > don't think the architecture allows SVE without FP, for obvious
> > reasons...
> 
> Good point, though now that I think about it I can't think of a
> requirement for FP when implementing SME (there's certainly not
> one for SVE).

Even if the architecture was allowing this madness, KVM doesn't allow
SVE if FP is not available, just like the rest of the kernel.

> There's no use for that hook now though.

Care to clarify?

	M.

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

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

  reply	other threads:[~2022-09-21 17:31 UTC|newest]

Thread overview: 46+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-08-15 22:55 [PATCH v3 0/7] arm64/sve: Clean up KVM integration and optimise syscalls Mark Brown
2022-08-15 22:55 ` Mark Brown
2022-08-15 22:55 ` [PATCH v3 1/7] KVM: arm64: Discard any SVE state when entering KVM guests Mark Brown
2022-08-15 22:55   ` Mark Brown
2022-09-20 16:44   ` Marc Zyngier
2022-09-20 16:44     ` Marc Zyngier
2022-09-20 20:21     ` Mark Brown
2022-09-20 20:21       ` Mark Brown
2022-09-21 17:31       ` Marc Zyngier [this message]
2022-09-21 17:31         ` Marc Zyngier
2022-09-22 11:44         ` Mark Brown
2022-09-22 11:44           ` Mark Brown
2022-08-15 22:55 ` [PATCH v3 2/7] arm64/fpsimd: Track the saved FPSIMD state type separately to TIF_SVE Mark Brown
2022-08-15 22:55   ` Mark Brown
2022-09-20 17:14   ` Marc Zyngier
2022-09-20 17:14     ` Marc Zyngier
2022-09-20 18:09     ` Mark Brown
2022-09-20 18:09       ` Mark Brown
2022-09-20 18:30       ` Marc Zyngier
2022-09-20 18:30         ` Marc Zyngier
2022-08-15 22:55 ` [PATCH v3 3/7] arm64/fpsimd: Have KVM explicitly say which FP registers to save Mark Brown
2022-08-15 22:55   ` Mark Brown
2022-09-20 17:52   ` Marc Zyngier
2022-09-20 17:52     ` Marc Zyngier
2022-09-20 18:32     ` Mark Brown
2022-09-20 18:32       ` Mark Brown
2022-09-21 17:47       ` Marc Zyngier
2022-09-21 17:47         ` Marc Zyngier
2022-09-22 12:18         ` Mark Brown
2022-09-22 12:18           ` Mark Brown
2022-08-15 22:55 ` [PATCH v3 4/7] arm64/fpsimd: Stop using TIF_SVE to manage register saving in KVM Mark Brown
2022-08-15 22:55   ` Mark Brown
2022-09-20 18:04   ` Marc Zyngier
2022-09-20 18:04     ` Marc Zyngier
2022-09-20 18:53     ` Mark Brown
2022-09-20 18:53       ` Mark Brown
2022-08-15 22:55 ` [PATCH v3 5/7] arm64/fpsimd: Load FP state based on recorded data type Mark Brown
2022-08-15 22:55   ` Mark Brown
2022-09-20 18:19   ` Marc Zyngier
2022-09-20 18:19     ` Marc Zyngier
2022-09-20 19:02     ` Mark Brown
2022-09-20 19:02       ` Mark Brown
2022-08-15 22:55 ` [PATCH v3 6/7] arm64/fpsimd: SME no longer requires SVE register state Mark Brown
2022-08-15 22:55   ` Mark Brown
2022-08-15 22:55 ` [PATCH v3 7/7] arm64/sve: Leave SVE enabled on syscall if we don't context switch Mark Brown
2022-08-15 22:55   ` Mark Brown

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