linux-kernel - Re: [PATCH 08/61] KVM: x86: Warn on zero-size save state for valid CPUID 0xD.N sub-leaf

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Date:   Fri, 7 Feb 2020 07:56:57 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 08/61] KVM: x86: Warn on zero-size save state for valid
 CPUID 0xD.N sub-leaf

On Fri, Feb 07, 2020 at 04:54:59PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@...el.com> writes:
> 
> > WARN if the save state size for a valid XCR0-managed sub-leaf is zero,
> > which would indicate a KVM or CPU bug.  Add a comment to explain why KVM
> > WARNs so the reader doesn't have to tease out the relevant bits from
> > Intel's SDM and KVM's XCR0/XSS code.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > ---
> >  arch/x86/kvm/cpuid.c | 13 ++++++++++---
> >  1 file changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index fd9b29aa7abc..424dde41cb5d 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -677,10 +677,17 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
> >  				goto out;
> >  
> >  			do_host_cpuid(&entry[i], function, idx);
> > -			if (entry[i].eax == 0)
> > -				continue;
> > -			if (WARN_ON_ONCE(entry[i].ecx & 1))
> > +
> > +			/*
> > +			 * The @supported check above should have filtered out
> > +			 * invalid sub-leafs as well as sub-leafs managed by
> 
> Is it 'sub-leafs' or 'sub-leaves' actually? :-)

Yes.  :-D