linux-kernel - [PATCH] KVM: VMX: Do not trap VMFUNC instructions for L1 guests.

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Date:   Mon,  7 Nov 2022 16:27:27 +0800
From:   Yu Zhang <yu.c.zhang@...ux.intel.com>
To:     pbonzini@...hat.com, seanjc@...gle.com, kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] KVM: VMX: Do not trap VMFUNC instructions for L1 guests.

VMFUNC is not supported for L1 guests, and executing VMFUNC in
L1 shall generate a #UD directly. Just disable it in secondary
proc-based execution control for L1, instead of intercepting it
and inject the #UD again.

Signed-off-by: Yu Zhang <yu.c.zhang@...ux.intel.com>
---
 arch/x86/kvm/vmx/nested.c | 17 +++++------------
 arch/x86/kvm/vmx/vmx.c    |  4 +++-
 2 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 0c62352dda6a..8858c6c0979f 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5793,11 +5793,11 @@ static int handle_vmfunc(struct kvm_vcpu *vcpu)
 	u32 function = kvm_rax_read(vcpu);
 
 	/*
-	 * VMFUNC is only supported for nested guests, but we always enable the
-	 * secondary control for simplicity; for non-nested mode, fake that we
-	 * didn't by injecting #UD.
+	 * VMFUNC is only supported for nested guests, instead of triggering
+	 * a VM Exit, non-nested guests shall receive #UD directly.
 	 */
 	if (!is_guest_mode(vcpu)) {
+		vcpu_unimpl(vcpu, "vmx: unexpected vm exit EXIT_REASON_VMFUNC.\n");
 		kvm_queue_exception(vcpu, UD_VECTOR);
 		return 1;
 	}
@@ -6808,6 +6808,7 @@ void nested_vmx_setup_ctls_msrs(struct vmcs_config *vmcs_conf, u32 ept_caps)
 		SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
 		SECONDARY_EXEC_RDRAND_EXITING |
 		SECONDARY_EXEC_ENABLE_INVPCID |
+		SECONDARY_EXEC_ENABLE_VMFUNC |
 		SECONDARY_EXEC_RDSEED_EXITING |
 		SECONDARY_EXEC_XSAVES |
 		SECONDARY_EXEC_TSC_SCALING;
@@ -6839,16 +6840,8 @@ void nested_vmx_setup_ctls_msrs(struct vmcs_config *vmcs_conf, u32 ept_caps)
 				SECONDARY_EXEC_ENABLE_PML;
 			msrs->ept_caps |= VMX_EPT_AD_BIT;
 		}
-	}
 
-	if (cpu_has_vmx_vmfunc()) {
-		msrs->secondary_ctls_high |=
-			SECONDARY_EXEC_ENABLE_VMFUNC;
-		/*
-		 * Advertise EPTP switching unconditionally
-		 * since we emulate it
-		 */
-		if (enable_ept)
+		if (cpu_has_vmx_vmfunc())
 			msrs->vmfunc_controls =
 				VMX_VMFUNC_EPTP_SWITCHING;
 	}
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 65f092e4a81b..9e17de62eb37 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -4483,6 +4483,9 @@ static u32 vmx_secondary_exec_control(struct vcpu_vmx *vmx)
 				  SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY);
 	exec_control &= ~SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE;
 
+	/* VMFUNC is not supported for L1 guest, just disable it. */
+	exec_control &= ~SECONDARY_EXEC_ENABLE_VMFUNC;
+
 	/* SECONDARY_EXEC_DESC is enabled/disabled on writes to CR4.UMIP,
 	 * in vmx_set_cr4.  */
 	exec_control &= ~SECONDARY_EXEC_DESC;
@@ -6000,7 +6003,6 @@ static int (*kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
 	[EXIT_REASON_RDSEED]                  = kvm_handle_invalid_op,
 	[EXIT_REASON_PML_FULL]		      = handle_pml_full,
 	[EXIT_REASON_INVPCID]                 = handle_invpcid,
-	[EXIT_REASON_VMFUNC]		      = handle_vmx_instruction,
 	[EXIT_REASON_PREEMPTION_TIMER]	      = handle_preemption_timer,
 	[EXIT_REASON_ENCLS]		      = handle_encls,
 	[EXIT_REASON_BUS_LOCK]                = handle_bus_lock_vmexit,
-- 
2.17.1