linux-kernel - [PATCH v3 4/4] KVM: SVM: Support #GP handling for the case of nested on nested

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Date:   Tue, 26 Jan 2021 03:18:31 -0500
From:   Wei Huang <wei.huang2@....com>
To:     kvm@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, pbonzini@...hat.com,
        vkuznets@...hat.com, mlevitsk@...hat.com, seanjc@...gle.com,
        joro@...tes.org, bp@...en8.de, tglx@...utronix.de,
        mingo@...hat.com, x86@...nel.org, jmattson@...gle.com,
        wanpengli@...cent.com, bsd@...hat.com, dgilbert@...hat.com,
        luto@...capital.net, wei.huang2@....com
Subject: [PATCH v3 4/4] KVM: SVM: Support #GP handling for the case of nested on nested

Under the case of nested on nested (L0->L1->L2->L3), #GP triggered by
SVM instructions can be hided from L1. Instead the hypervisor can
inject the proper #VMEXIT to inform L1 of what is happening. Thus L1
can avoid invoking the #GP workaround. For this reason we turns on
guest VM's X86_FEATURE_SVME_ADDR_CHK bit for KVM running inside VM to
receive the notification and change behavior.

Similarly we check if vcpu is under guest mode before emulating the
vmware-backdoor instructions. For the case of nested on nested, we
let the guest handle it.

Co-developed-by: Bandan Das <bsd@...hat.com>
Signed-off-by: Bandan Das <bsd@...hat.com>
Signed-off-by: Wei Huang <wei.huang2@....com>
Tested-by: Maxim Levitsky <mlevitsk@...hat.com>
Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index f9233c79265b..83c401d2709f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -929,6 +929,9 @@ static __init void svm_set_cpu_caps(void)
 
 		if (npt_enabled)
 			kvm_cpu_cap_set(X86_FEATURE_NPT);
+
+		/* Nested VM can receive #VMEXIT instead of triggering #GP */
+		kvm_cpu_cap_set(X86_FEATURE_SVME_ADDR_CHK);
 	}
 
 	/* CPUID 0x80000008 */
@@ -2198,6 +2201,11 @@ static int svm_instr_opcode(struct kvm_vcpu *vcpu)
 
 static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 {
+	const int guest_mode_exit_codes[] = {
+		[SVM_INSTR_VMRUN] = SVM_EXIT_VMRUN,
+		[SVM_INSTR_VMLOAD] = SVM_EXIT_VMLOAD,
+		[SVM_INSTR_VMSAVE] = SVM_EXIT_VMSAVE,
+	};
 	int (*const svm_instr_handlers[])(struct vcpu_svm *svm) = {
 		[SVM_INSTR_VMRUN] = vmrun_interception,
 		[SVM_INSTR_VMLOAD] = vmload_interception,
@@ -2205,7 +2213,14 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 	};
 	struct vcpu_svm *svm = to_svm(vcpu);
 
-	return svm_instr_handlers[opcode](svm);
+	if (is_guest_mode(vcpu)) {
+		svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode];
+		svm->vmcb->control.exit_info_1 = 0;
+		svm->vmcb->control.exit_info_2 = 0;
+
+		return nested_svm_vmexit(svm);
+	} else
+		return svm_instr_handlers[opcode](svm);
 }
 
 /*
@@ -2239,7 +2254,8 @@ static int gp_interception(struct vcpu_svm *svm)
 		 * VMware backdoor emulation on #GP interception only handles
 		 * IN{S}, OUT{S}, and RDPMC.
 		 */
-		return kvm_emulate_instruction(vcpu,
+		if (!is_guest_mode(vcpu))
+			return kvm_emulate_instruction(vcpu,
 				EMULTYPE_VMWARE_GP | EMULTYPE_NO_DECODE);
 	} else
 		return emulate_svm_instr(vcpu, opcode);
-- 
2.27.0