linux-kernel - [PATCH v4 2/2] KVM: VMX: Fix VPID capability detection

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Date:   Wed, 18 Oct 2017 16:02:19 -0700
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: [PATCH v4 2/2] KVM: VMX: Fix VPID capability detection

From: Wanpeng Li <wanpeng.li@...mail.com>

In my setup, EPT is not exposed to L1, the VPID capability is exposed and 
can be observed by vmxcap tool in L1:
INVVPID supported                        yes
Individual-address INVVPID               yes
Single-context INVVPID                   yes
All-context INVVPID                      yes
Single-context-retaining-globals INVVPID yes

However, the module parameter of VPID observed in L1 is always N, the
cpu_has_vmx_invvpid() check in L1 KVM fails since vmx_capability.vpid
is 0 and it is not read from MSR due to EPT is not exposed. 

The VPID can be used to tag linear mappings when EPT is not enabled. However,
current logic just detects VPID capability if EPT is enabled, this patch
fixes it.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
v3 -> v4:
 * clear vmx_capability.ept/vmx_capability.vpid along with the warnings
v2 -> v3:
 * add pr_warn_once
v1 -> v2:
 * rdmsr_safe instead of rdmsr
 * add more explanation to patch description

 arch/x86/kvm/vmx.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 3644540..be7ad1c 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3681,14 +3681,25 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
 				SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
 				SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
 
+	rdmsr_safe(MSR_IA32_VMX_EPT_VPID_CAP,
+		&vmx_capability.ept, &vmx_capability.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);
-		rdmsr(MSR_IA32_VMX_EPT_VPID_CAP,
-		      vmx_capability.ept, vmx_capability.vpid);
+	} else if (vmx_capability.ept) {
+		vmx_capability.ept = 0;
+		pr_warn_once("EPT CAP should not exist if not support "
+				"1-setting enable EPT VM-execution control\n");
+	}
+	if (!(_cpu_based_2nd_exec_control & SECONDARY_EXEC_ENABLE_VPID) &&
+		vmx_capability.vpid) {
+		vmx_capability.vpid = 0;
+		pr_warn_once("VPID CAP should not exist if not support "
+				"1-setting enable VPID VM-execution control\n");
 	}
 
 	min = VM_EXIT_SAVE_DEBUG_CONTROLS | VM_EXIT_ACK_INTR_ON_EXIT;
-- 
2.7.4