linux-kernel - Re: [PATCH RFC v1 03/10] KVM: VMX: Move CPU_BASED_{CR3_LOAD,CR3_STORE,INVLPG}_EXITING filtering out of setup_vmcs

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Date:   Fri, 24 Jun 2022 00:04:12 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Anirudh Rayabharam <anrayabh@...ux.microsoft.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v1 03/10] KVM: VMX: Move
 CPU_BASED_{CR3_LOAD,CR3_STORE,INVLPG}_EXITING filtering out of
 setup_vmcs_config()

On Wed, Jun 22, 2022, Vitaly Kuznetsov wrote:
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 01294a2fc1c1..4583de7f0324 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -4293,6 +4293,16 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
>  			  CPU_BASED_MONITOR_TRAP_FLAG |
>  			  CPU_BASED_PAUSE_EXITING);
>  
> +	if (vmcs_config.cpu_based_2nd_exec_ctrl & SECONDARY_EXEC_ENABLE_EPT) {
> +		/*
> +		 * CR3 accesses and invlpg don't need to cause VM Exits when EPT
> +		 * enabled.
> +		 */
> +		exec_control &= ~(CPU_BASED_CR3_LOAD_EXITING |
> +				  CPU_BASED_CR3_STORE_EXITING |
> +				  CPU_BASED_INVLPG_EXITING);
> +	}

No need to clear them based on support, just invert the logic so that KVM leaves
them set in the base config and then cleares them if EPT is enabled (instead of
clearing them if EPT is supported and then restoring them if EPT is disabled via
module param).

--
From: Sean Christopherson <seanjc@...gle.com>
Date: Thu, 23 Jun 2022 17:00:58 -0700
Subject: [PATCH] KVM: VMX: Clear controls obsoleted by EPT at runtime, not
 setup

Clear the CR3 and INVLPG interception controls at runtime based on
whether or not EPT is being _used_, as opposed to clearing the bits at
setup if EPT is _supported_ in hardware, and then restoring them when EPT
is not used.  Not mucking with the base config will allow using the base
config as the starting point for emulating the VMX capability MSRs.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/vmx/vmx.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 5d8f28b5d6ca..f39af86a6c50 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2550,13 +2550,8 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf,
 	rdmsr_safe(MSR_IA32_VMX_EPT_VPID_CAP,
 		&vmx_cap->ept, &vmx_cap->vpid);

-	if (_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_EPT) {
-		/* CR3 accesses and invlpg don't need to cause VM Exits when EPT
-		   enabled */
-		_cpu_based_exec_control &= ~(CPU_BASED_CR3_LOAD_EXITING |
-					     CPU_BASED_CR3_STORE_EXITING |
-					     CPU_BASED_INVLPG_EXITING);
-	} else if (vmx_cap->ept) {
+	if (!(_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_EPT) &&
+	    vmx_cap->ept) {
 		pr_warn_once("EPT CAP should not exist if not support "
 				"1-setting enable EPT VM-execution control\n");

@@ -4320,10 +4315,12 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
 				CPU_BASED_CR8_LOAD_EXITING;
 #endif
 	}
-	if (!enable_ept)
-		exec_control |= CPU_BASED_CR3_STORE_EXITING |
-				CPU_BASED_CR3_LOAD_EXITING  |
-				CPU_BASED_INVLPG_EXITING;
+
+	/* No need to intercept CR3 access or INVPLG when using EPT. */
+	if (enable_ept)
+		exec_control &= ~(CPU_BASED_CR3_LOAD_EXITING |
+				  CPU_BASED_CR3_STORE_EXITING |
+				  CPU_BASED_INVLPG_EXITING);
 	if (kvm_mwait_in_guest(vmx->vcpu.kvm))
 		exec_control &= ~(CPU_BASED_MWAIT_EXITING |
 				CPU_BASED_MONITOR_EXITING);

base-commit: d365a92177bda6629885401d44fbe912106b3df6
--