linux-kernel - Re: [PATCH 1/2] KVM: X86: Move ignore

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Message-ID: <df859fb0-a665-a82a-0cf1-8db95179cb74@redhat.com>
Date:   Thu, 25 Jun 2020 20:44:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     Peter Xu <peterx@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 1/2] KVM: X86: Move ignore_msrs handling upper the stack

On 25/06/20 18:25, Sean Christopherson wrote:
> I get the "what" of the change, and even the "why" to some extent, but I
> dislike the idea of supporting/encouraging blind reads/writes to MSRs.
> Blind writes are just asking for problems, and suppressing warnings on reads
> is almost guaranteed to be suppressing a KVM bug.

Right, that's why this patch does not just suppress warnings: it adds a
different return value to detect the case.

> TSC_CTRL aside, if we insist on pointing a gun at our foot at some point,
> this should be a dedicated flavor of MSR access, e.g. msr_data.kvm_initiated,
> so that it at least requires intentionally loading the gun.

With this patch, __kvm_get_msr does not know about ignore_msrs at all,
that seems to be strictly an improvement; do you agree with that?  What
would you think about adding warn_unused_result to __kvm_get_msr?

Paolo