linux-kernel - Re: [PATCH v5 1/3] KVM: nVMX: Sync L2 guest CET states between L1/L2

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Date:   Tue, 20 Apr 2021 17:35:01 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     pbonzini@...hat.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 1/3] KVM: nVMX: Sync L2 guest CET states between L1/L2

On Fri, Apr 09, 2021, Yang Weijiang wrote:
> These fields are rarely updated by L1 QEMU/KVM, sync them when L1 is trying to
> read/write them and after they're changed. If CET guest entry-load bit is not
> set by L1 guest, migrate them to L2 manaully.
> 
> Opportunistically remove one blank line in previous patch.
> 
> Suggested-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> ---
>  arch/x86/kvm/cpuid.c      |  1 -
>  arch/x86/kvm/vmx/nested.c | 30 ++++++++++++++++++++++++++++++
>  arch/x86/kvm/vmx/vmx.h    |  3 +++
>  3 files changed, 33 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index d191de769093..8692f53b8cd0 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -143,7 +143,6 @@ void kvm_update_cpuid_runtime(struct kvm_vcpu *vcpu)
>  		}
>  		vcpu->arch.guest_supported_xss =
>  			(((u64)best->edx << 32) | best->ecx) & supported_xss;
> -
>  	} else {
>  		vcpu->arch.guest_supported_xss = 0;
>  	}
> diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
> index 9728efd529a1..87beb1c034e1 100644
> --- a/arch/x86/kvm/vmx/nested.c
> +++ b/arch/x86/kvm/vmx/nested.c
> @@ -2516,6 +2516,13 @@ static void prepare_vmcs02_rare(struct vcpu_vmx *vmx, struct vmcs12 *vmcs12)
>  	vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, vmx->msr_autoload.guest.nr);
>  
>  	set_cr4_guest_host_mask(vmx);
> +
> +	if (kvm_cet_supported() && vmx->nested.nested_run_pending &&
> +	    (vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)) {
> +		vmcs_writel(GUEST_SSP, vmcs12->guest_ssp);
> +		vmcs_writel(GUEST_S_CET, vmcs12->guest_s_cet);
> +		vmcs_writel(GUEST_INTR_SSP_TABLE, vmcs12->guest_ssp_tbl);
> +	}
>  }
>  
>  /*
> @@ -2556,6 +2563,15 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
>  	if (kvm_mpx_supported() && (!vmx->nested.nested_run_pending ||
>  	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS)))
>  		vmcs_write64(GUEST_BNDCFGS, vmx->nested.vmcs01_guest_bndcfgs);
> +
> +	if (kvm_cet_supported() && (!vmx->nested.nested_run_pending ||
> +	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE))) {
> +		vmcs_writel(GUEST_SSP, vmx->nested.vmcs01_guest_ssp);
> +		vmcs_writel(GUEST_S_CET, vmx->nested.vmcs01_guest_s_cet);
> +		vmcs_writel(GUEST_INTR_SSP_TABLE,
> +			    vmx->nested.vmcs01_guest_ssp_tbl);
> +	}
> +
>  	vmx_set_rflags(vcpu, vmcs12->guest_rflags);
>  
>  	/* EXCEPTION_BITMAP and CR0_GUEST_HOST_MASK should basically be the
> @@ -3375,6 +3391,11 @@ enum nvmx_vmentry_status nested_vmx_enter_non_root_mode(struct kvm_vcpu *vcpu,
>  	if (kvm_mpx_supported() &&
>  		!(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_BNDCFGS))
>  		vmx->nested.vmcs01_guest_bndcfgs = vmcs_read64(GUEST_BNDCFGS);
> +	if (kvm_cet_supported() && !vmx->nested.nested_run_pending) {

This needs to be:

	if (kvm_cet_supported() && (!vmx->nested.nested_run_pending ||
	    !(vmcs12->vm_entry_controls & VM_ENTRY_LOAD_CET_STATE)))

otherwise the vmcs01_* members will be stale when emulating VM-Enter with
vcmc12.vm_entry_controls.LOAD_CET_STATE=0.

> +		vmx->nested.vmcs01_guest_ssp = vmcs_readl(GUEST_SSP);
> +		vmx->nested.vmcs01_guest_s_cet = vmcs_readl(GUEST_S_CET);
> +		vmx->nested.vmcs01_guest_ssp_tbl = vmcs_readl(GUEST_INTR_SSP_TABLE);
> +	}