linux-kernel - Re: [PATCH v2 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT

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Message-ID: <c9f5050a-6144-adbc-25ef-8a7543176ac6@redhat.com>
Date:   Wed, 29 May 2019 03:29:55 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Tao Xu <tao3.xu@...el.com>, rkrcmar@...hat.com, corbet@....net,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, hpa@...or.com,
        sean.j.christopherson@...el.com
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, jingqi.liu@...el.com
Subject: Re: [PATCH v2 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL

On 24/05/19 09:56, Tao Xu wrote:
> +
> +	if (rdmsrl_safe(MSR_IA32_UMWAIT_CONTROL, &host_umwait_control))
> +		return;
> +

Does the host value ever change?  If not, this can perhaps be read once
when kvm_intel is loaded.  And if it changes often, it should be
shadowed into a percpu variable.

Paolo