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

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Message-ID: <4f5a7fca-02b3-4cd9-159c-59fcda3debd0@redhat.com>
Date:   Mon, 15 Jun 2020 15:46:53 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Jim Mattson <jmattson@...gle.com>, Babu Moger <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.

Paolo