linux-kernel - Re: [PATCH 02/15] KVM: VMX: Avoid to rdmsrl(MSR_IA32_SYSENTER

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Date:   Thu, 18 Nov 2021 15:38:31 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        linux-kernel@...r.kernel.org
Cc:     kvm@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 02/15] KVM: VMX: Avoid to rdmsrl(MSR_IA32_SYSENTER_ESP)

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