linux-kernel - Re: [RESEND] Atomic switch of MSR_IA32_UMWAIT

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Date:   Thu, 23 Jan 2020 17:16:21 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Tao Xu <tao3.xu@...el.com>, Jingqi Liu <jingqi.liu@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RESEND] Atomic switch of MSR_IA32_UMWAIT_CONTROL

On 23/01/20 16:45, Sean Christopherson wrote:
> cc'ing KVM and LKML this time...
> 
> Why does KVM use the atomic load/store lists to load MSR_IA32_UMWAIT_CONTROL
> on VM-Enter/VM-Exit?  Unless the host kernel is doing UWMAIT, which it
> really shouldn't and AFAICT doesn't, isn't it better to use the shared MSR
> mechanism to load the host value only when returning to userspace, and
> reload the guest value on demand?
> 

To clarify, laziness also on part of the reviewer, aka me.

Paolo