linux-kernel - Re: [PATCH 2/4] KVM: VMX: Setup MSR bitmap only when has msr

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Date:   Tue, 15 Oct 2019 17:40:33 -0700
From:   Krish Sadhukhan <krish.sadhukhan@...cle.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] KVM: VMX: Setup MSR bitmap only when has msr_bitmap
 capability



On 10/15/2019 09:40 AM, Xiaoyao Li wrote:
> Move the MSR bitmap setup codes to vmx_vmcs_setup() and only setup them
> when hardware has msr_bitmap capability.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
> ---
>   arch/x86/kvm/vmx/vmx.c | 39 ++++++++++++++++++++-------------------
>   1 file changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 58b77a882426..7051511c27c2 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4164,12 +4164,30 @@ static void ept_set_mmio_spte_mask(void)
>   static void vmx_vmcs_setup(struct vcpu_vmx *vmx)
>   {
>   	int i;
> +	unsigned long *msr_bitmap;
>   
>   	if (nested)
>   		nested_vmx_vmcs_setup();
>   
> -	if (cpu_has_vmx_msr_bitmap())
> -		vmcs_write64(MSR_BITMAP, __pa(vmx->vmcs01.msr_bitmap));
> +	if (cpu_has_vmx_msr_bitmap()) {
> +		msr_bitmap = vmx->vmcs01.msr_bitmap;
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_TSC, MSR_TYPE_R);

vmx_disable_intercept_for_msr() also calls cpu_has_vmx_msr_bitmap(), 
which means we are repeating the check. A cleaner approach is to remove 
the call to cpu_has_vmx_msr_bitmap()  from 
vmx_disable_intercept_for_msr()  and let its callers do the check just 
like you are doing here.

> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_FS_BASE, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_GS_BASE, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_CS, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW);
> +		vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW);
> +		if (kvm_cstate_in_guest(vmx->vcpu.kvm)) {
> +			vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C1_RES, MSR_TYPE_R);
> +			vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C3_RESIDENCY, MSR_TYPE_R);
> +			vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
> +			vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
> +		}
> +
> +		vmcs_write64(MSR_BITMAP, __pa(msr_bitmap));
> +	}
> +	vmx->msr_bitmap_mode = 0;
>   
>   	vmcs_write64(VMCS_LINK_POINTER, -1ull); /* 22.3.1.5 */
>   
> @@ -6697,7 +6715,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>   {
>   	int err;
>   	struct vcpu_vmx *vmx;
> -	unsigned long *msr_bitmap;
>   	int cpu;
>   
>   	BUILD_BUG_ON_MSG(offsetof(struct vcpu_vmx, vcpu) != 0,
> @@ -6754,22 +6771,6 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
>   	if (err < 0)
>   		goto free_msrs;
>   
> -	msr_bitmap = vmx->vmcs01.msr_bitmap;
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_TSC, MSR_TYPE_R);
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_FS_BASE, MSR_TYPE_RW);
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_GS_BASE, MSR_TYPE_RW);
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_KERNEL_GS_BASE, MSR_TYPE_RW);
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_CS, MSR_TYPE_RW);
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_ESP, MSR_TYPE_RW);
> -	vmx_disable_intercept_for_msr(msr_bitmap, MSR_IA32_SYSENTER_EIP, MSR_TYPE_RW);
> -	if (kvm_cstate_in_guest(kvm)) {
> -		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C1_RES, MSR_TYPE_R);
> -		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C3_RESIDENCY, MSR_TYPE_R);
> -		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C6_RESIDENCY, MSR_TYPE_R);
> -		vmx_disable_intercept_for_msr(msr_bitmap, MSR_CORE_C7_RESIDENCY, MSR_TYPE_R);
> -	}
> -	vmx->msr_bitmap_mode = 0;
> -
>   	vmx->loaded_vmcs = &vmx->vmcs01;
>   	cpu = get_cpu();
>   	vmx_vcpu_load(&vmx->vcpu, cpu);