linux-kernel - Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT

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Message-ID: <3642373d-8d1d-de80-d3db-e835a8f29449@redhat.com>
Date:   Thu, 21 May 2020 10:40:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tao Xu <tao3.xu@...el.com>, Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Maxim Levitsky <mlevitsk@...hat.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] kvm/x86: don't expose MSR_IA32_UMWAIT_CONTROL
 unconditionally

On 21/05/20 08:44, Tao Xu wrote:
> 
> I am sorry, I mean:
> By default, we don't expose WAITPKG to guest. For QEMU, we can use
> "-overcommit cpu-pm=on" to use WAITPKG.

But UMONITOR, UMWAIT and TPAUSE are not NOPs on older processors (which
I should have checked before committing your patch, I admit).  So you
have broken "-cpu host -overcommit cpu-pm=on" on any processor that
doesn't have WAITPKG.  I'll send a patch.

Paolo