linux-kernel - [PATCH v3 2/7] KVM: x86: nSVM: restore the L1 host state prior to resuming nested guest on SMM exit

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Date:   Mon, 13 Sep 2021 17:09:49 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH v3 2/7] KVM: x86: nSVM: restore the L1 host state prior to resuming nested guest on SMM exit

Otherwise guest entry code might see incorrect L1 state (e.g paging state).

Fixes: 37be407b2ce8 ("KVM: nSVM: Fix L1 state corruption upon return from SMM")

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/svm.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index a75dafbfa4a6..e3b092a3a2e1 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4358,10 +4358,6 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
 	if (svm_allocate_nested(svm))
 		goto unmap_save;
 
-	vmcb12 = map.hva;
-	nested_load_control_from_vmcb12(svm, &vmcb12->control);
-	ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12);
-
 	/*
 	 * Restore L1 host state from L1 HSAVE area as VMCB01 was
 	 * used during SMM (see svm_enter_smm())
@@ -4369,6 +4365,14 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
 
 	svm_copy_vmrun_state(&svm->vmcb01.ptr->save, map_save.hva + 0x400);
 
+	/*
+	 * Enter the nested guest now
+	 */
+
+	vmcb12 = map.hva;
+	nested_load_control_from_vmcb12(svm, &vmcb12->control);
+	ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12);
+
 unmap_save:
 	kvm_vcpu_unmap(vcpu, &map_save, true);
 unmap_map:
-- 
2.26.3