linux-kernel - Re: [PATCH 39/61] KVM: SVM: Convert feature updates from CPUID to KVM cpu caps

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Date:   Thu, 27 Feb 2020 16:36:14 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 39/61] KVM: SVM: Convert feature updates from CPUID to
 KVM cpu caps

On Thu, Feb 27, 2020 at 04:28:33PM -0800, Sean Christopherson wrote:
> On Tue, Feb 25, 2020 at 04:10:18PM +0100, Paolo Bonzini wrote:
> > On 01/02/20 19:51, Sean Christopherson wrote:
> > > +	/* CPUID 0x8000000A */
> > > +	/* Support next_rip if host supports it */
> > > +	if (boot_cpu_has(X86_FEATURE_NRIPS))
> > > +		kvm_cpu_cap_set(X86_FEATURE_NRIPS);
> > 
> > Should this also be conditional on "nested"?
> 
> I think that makes sense?  AFAICT it should probably be conditional on
> "nrips" as well.  X86_FEATURE_NPT should also be conditional on "nested".
> I'll tack on a patch to make those changes, the cleanup is easier without
> the things spread across different case statements, e.g. wrap the entire
> SVM feature leaf in "if (nested)".

Regarding NRIPS, the original commit added the "Support next_rip if host
supports it" comment, but I can't tell is "host supports" means "supported
in hardware" or "supported by KVM".  In other words, should I make the cap
dependent "nrips" or leave it as is?