linux-kernel - Re: [PATCH 06/13] KVM: SVM: Add VNMI bit definition

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Message-ID: <Y3aaqJo7ckdUsyde@google.com>
Date:   Thu, 17 Nov 2022 20:33:44 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sandipan Das <sandipan.das@....com>,
        Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
        Jing Liu <jing2.liu@...el.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Wyes Karny <wyes.karny@....com>,
        Babu Moger <babu.moger@....com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Jim Mattson <jmattson@...gle.com>, x86@...nel.org,
        Santosh Shukla <santosh.shukla@....com>
Subject: Re: [PATCH 06/13] KVM: SVM: Add VNMI bit definition

On Thu, Nov 17, 2022, Borislav Petkov wrote:
> On Thu, Nov 17, 2022 at 04:42:57PM +0000, Sean Christopherson wrote:
> > Why? This is rarely run code, won't cpu_feature_enabled()
> > unnecessarily require patching?
> 
> Because we want one single interface to test X86_FEATURE flags. And
> there's no need for the users to know whether it wants patching or not -
> we simply patch *everywhere* and that's it.
> 
> > And while we're on the topic... https://lore.kernel.org/all/Y22IzA9DN%2FxYWgWN@google.com
> 
> Because static_ or boot_ is not relevant to the user - all she
> wants to know is whether a cpu feature has been enabled. Thus
> cpu_feature_enabled().
> 
> And yes, at the time I protested a little about unnecessary patching.
> And tglx said "Why not?". And I had no good answer to that. So we can
> just as well patch *everywhere*.

Ah, I missed that memo.


Paolo,

Since it sounds like static_cpu_has() is going the way of the dodo, and ditto for
boot_cpu_has() except for flows that don't play nice with patching (none of which
are in KVM), should we do a KVM-wide conversion to cpu_feature_enabled() at some
point in the near future?