Message-ID: <42820429-f09d-2576-50c4-5ecb74f49891@redhat.com>
Date:   Thu, 18 Nov 2021 15:38:31 +0100
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Subject: Re: [PATCH 02/15] KVM: VMX: Avoid to rdmsrl(MSR_IA32_SYSENTER_ESP)
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To:     Lai Jiangshan <laijs@linux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@gmail.com>,
        linux-kernel@vger.kernel.org
Cc:     kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>
References: <20211118110814.2568-1-jiangshanlai@gmail.com>
 <20211118110814.2568-3-jiangshanlai@gmail.com>
 <94d4b7d8-1e56-69e9-dd52-d154bee6c461@redhat.com>
 <e2c646a1-7e02-5dc5-0f02-1b4247772a69@linux.alibaba.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
In-Reply-To: <e2c646a1-7e02-5dc5-0f02-1b4247772a69@linux.alibaba.com>
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On 11/18/21 15:17, Lai Jiangshan wrote:
> 
> The change in vmx_vcpu_load_vmcs() handles only the percpu constant case:
> (cpu_entry_stack(cpu) + 1), it doesn't handle the case where
> MSR_IA32_SYSENTER_ESP is NULL.
> 
> The change in vmx_set_constant_host_state() handles the case where
> MSR_IA32_SYSENTER_ESP is NULL, it does be constant host state in this case.
> If it is not the case, the added code in vmx_vcpu_load_vmcs() will override
> it safely.
> 
> If an else branch with "vmcs_writel(HOST_IA32_SYSENTER_ESP, 0);" is 
> added to
> vmx_vcpu_load_vmcs(), we will not need to change 
> vmx_set_constant_host_state().

We can change vmx_set_constant_host_state to write 0.

Paolo