Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: [PATCH v2 2/3] KVM: vmx: Emulate MSR IA32_UMWAIT_CONTROL
To:     Tao Xu <tao3.xu@intel.com>, rkrcmar@redhat.com, corbet@lwn.net,
        tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
        sean.j.christopherson@intel.com
Cc:     x86@kernel.org, kvm@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, jingqi.liu@intel.com
References: <20190524075637.29496-1-tao3.xu@intel.com>
 <20190524075637.29496-3-tao3.xu@intel.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <c9f5050a-6144-adbc-25ef-8a7543176ac6@redhat.com>
Date:   Wed, 29 May 2019 03:29:55 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101
 Thunderbird/60.6.1
MIME-Version: 1.0
In-Reply-To: <20190524075637.29496-3-tao3.xu@intel.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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