linux-kernel - Re: [PATCH] kvm: x86: rewrite kvm_spec_ctrl_valid

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Date:   Tue, 7 Jul 2020 19:26:02 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Maxim Levitsky <mlevitsk@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        linux-kernel@...r.kernel.org, Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH] kvm: x86: rewrite kvm_spec_ctrl_valid_bits

On 07/07/20 13:35, Maxim Levitsky wrote:
> After thinking about this, I am thinking that we should apply similiar logic
> as done with the 'cpu-pm' related features.
> This way the user can choose between passing through the IA32_SPEC_CTRL,
> (and in this case, we can since the user choose it, pass it right away, and thus
> avoid using kvm_spec_ctrl_valid_bits completely), and between correctness,
> in which case we can always emulate this msr, and therefore check all the bits,
> both regard to guest and host supported values.

Unfortunately, passing it through is just too slow.  So I think it's
overkill.  There's two ways to deal with badly-behaved guests blocking
migration: 1) hide SPEC_CTRL altogether 2) kill them when migration
fails; both are acceptable depending on the situation.

Paolo

> Does this makes sense, or do you think that this is overkill?