linux-kernel - RE: [PATCH 3/3] KVM:SVM: Enable INVPCID feature on AMD

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Date:   Mon, 15 Jun 2020 09:59:09 -0500
From:   Babu Moger <babu.moger@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>, Joerg Roedel <joro@...tes.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>
Subject: RE: [PATCH 3/3] KVM:SVM: Enable INVPCID feature on AMD



> -----Original Message-----
> From: Paolo Bonzini <pbonzini@...hat.com>
> Sent: Monday, June 15, 2020 8:47 AM
> To: Jim Mattson <jmattson@...gle.com>; Moger, Babu
> <Babu.Moger@....com>
> Cc: Wanpeng Li <wanpengli@...cent.com>; Joerg Roedel <joro@...tes.org>;
> the arch/x86 maintainers <x86@...nel.org>; Sean Christopherson
> <sean.j.christopherson@...el.com>; Ingo Molnar <mingo@...hat.com>;
> Borislav Petkov <bp@...en8.de>; H . Peter Anvin <hpa@...or.com>; Vitaly
> Kuznetsov <vkuznets@...hat.com>; Thomas Gleixner <tglx@...utronix.de>;
> LKML <linux-kernel@...r.kernel.org>; kvm list <kvm@...r.kernel.org>
> Subject: Re: [PATCH 3/3] KVM:SVM: Enable INVPCID feature on AMD
> 
> On 13/06/20 02:04, Jim Mattson wrote:
> >> I think I have misunderstood this part. I was not inteding to change the
> >> #GP behaviour. I will remove this part. My intension of these series is to
> >> handle invpcid in shadow page mode. I have verified that part. Hope I did
> >> not miss anything else.
> > You don't really have to intercept INVPCID when tdp is in use, right?
> > There are certainly plenty of operations for which kvm does not
> > properly raise #UD when they aren't enumerated in the guest CPUID.
> >
> 
> Indeed; for RDRAND and RDSEED it makes sense to do so because the
> instructions may introduce undesirable nondeterminism (or block all the
> packages in your core as they have been doing for a few weeks).
> Therefore on Intel we trap them and raise #UD; on AMD this is not
> possible because RDRAND has no intercept.
> 
> In general however we do not try to hard to raise #UD and that is
> usually not even possible.

Yes. Sure. Thanks.
> 
> Paolo