linux-kernel - [PATCH v2 1/3] KVM: nSVM: restore the L1 host state prior to resuming a nested guest on SMM exit

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Message-Id: <20210823114618.1184209-2-mlevitsk@redhat.com>
Date:   Mon, 23 Aug 2021 14:46:16 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jim Mattson <jmattson@...gle.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT)), Wanpeng Li <wanpengli@...cent.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <seanjc@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: [PATCH v2 1/3] KVM: nSVM: restore the L1 host state prior to resuming a nested guest on SMM exit

If the guest is entered prior to restoring the host save area,
the guest entry code might see incorrect L1 state (e.g paging state).

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 1a70e11f0487..ea7a4dacd42f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4347,27 +4347,30 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
 					 gpa_to_gfn(vmcb12_gpa), &map) == -EINVAL)
 				return 1;
 
-			if (svm_allocate_nested(svm))
+			if (kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.hsave_msr),
+					 &map_save) == -EINVAL)
 				return 1;
 
-			vmcb12 = map.hva;
-
-			nested_load_control_from_vmcb12(svm, &vmcb12->control);
-
-			ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12);
-			kvm_vcpu_unmap(vcpu, &map, true);
+			if (svm_allocate_nested(svm))
+				return 1;
 
 			/*
 			 * Restore L1 host state from L1 HSAVE area as VMCB01 was
 			 * used during SMM (see svm_enter_smm())
 			 */
-			if (kvm_vcpu_map(vcpu, gpa_to_gfn(svm->nested.hsave_msr),
-					 &map_save) == -EINVAL)
-				return 1;
 
 			svm_copy_vmrun_state(&svm->vmcb01.ptr->save,
 					     map_save.hva + 0x400);
 
+			/*
+			 * Restore L2 state
+			 */
+
+			vmcb12 = map.hva;
+			nested_load_control_from_vmcb12(svm, &vmcb12->control);
+			ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12);
+
+			kvm_vcpu_unmap(vcpu, &map, true);
 			kvm_vcpu_unmap(vcpu, &map_save, true);
 		}
 	}
-- 
2.26.3