linux-kernel - Re: [PATCH AUTOSEL 4.19 08/26] kvm: x86: Improve emulation of CPUID leaves 0BH and 1FH

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Message-ID: <5fcb0e38-3542-dd39-6a1c-449b4f9f435e@redhat.com>
Date:   Wed, 9 Oct 2019 22:58:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sasha Levin <sashal@...nel.org>, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>, Marc Orr <marcorr@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Jacob Xu <jacobhxu@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 4.19 08/26] kvm: x86: Improve emulation of CPUID
 leaves 0BH and 1FH

On 09/10/19 19:05, Sasha Levin wrote:
> From: Jim Mattson <jmattson@...gle.com>
> 
> [ Upstream commit 43561123ab3759eb6ff47693aec1a307af0aef83 ]
> 
> For these CPUID leaves, the EDX output is not dependent on the ECX
> input (i.e. the SIGNIFCANT_INDEX flag doesn't apply to
> EDX). Furthermore, the low byte of the ECX output is always identical
> to the low byte of the ECX input. KVM does not produce the correct ECX
> and EDX outputs for any undefined subleaves beyond the first.
> 
> Special-case these CPUID leaves in kvm_cpuid, so that the ECX and EDX
> outputs are properly generated for all undefined subleaves.
> 
> Fixes: 0771671749b59a ("KVM: Enhance guest cpuid management")
> Fixes: a87f2d3a6eadab ("KVM: x86: Add Intel CPUID.1F cpuid emulation support")
> Signed-off-by: Jim Mattson <jmattson@...gle.com>
> Reviewed-by: Marc Orr <marcorr@...gle.com>
> Reviewed-by: Peter Shier <pshier@...gle.com>
> Reviewed-by: Jacob Xu <jacobhxu@...gle.com>
> Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  arch/x86/kvm/cpuid.c | 83 +++++++++++++++++++++++++-------------------
>  1 file changed, 47 insertions(+), 36 deletions(-)

This is absolutely not stable material.  Is it possible for KVM to opt
out of this AUTOSEL nonsense?

Paolo