linux-kernel - [PATCH v2 44/46] KVM: SVM: Emulate #INIT in response to triple fault shutdown

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Date:   Tue, 13 Jul 2021 09:33:22 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Reiji Watanabe <reijiw@...gle.com>
Subject: [PATCH v2 44/46] KVM: SVM: Emulate #INIT in response to triple fault shutdown

Emulate a full #INIT instead of simply initializing the VMCB if the
guest hits a shutdown.  Initializing the VMCB but not other vCPU state,
much of which is mirrored by the VMCB, results in incoherent and broken
vCPU state.

Ideally, KVM would not automatically init anything on shutdown, and
instead put the vCPU into e.g. KVM_MP_STATE_UNINITIALIZED and force
userspace to explicitly INIT or RESET the vCPU.  Even better would be to
add KVM_MP_STATE_SHUTDOWN, since technically NMI can break shutdown
(and SMI on Intel CPUs).

But, that ship has sailed, and emulating #INIT is the next best thing as
that has at least some connection with reality since there exist bare
metal platforms that automatically INIT the CPU if it hits shutdown.

Fixes: 46fe4ddd9dbb ("[PATCH] KVM: SVM: Propagate cpu shutdown events to userspace")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 10 +++++++---
 arch/x86/kvm/x86.c     |  1 +
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ea4bea428078..285587a7fe80 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2058,11 +2058,15 @@ static int shutdown_interception(struct kvm_vcpu *vcpu)
 		return -EINVAL;
 
 	/*
-	 * VMCB is undefined after a SHUTDOWN intercept
-	 * so reinitialize it.
+	 * VMCB is undefined after a SHUTDOWN intercept.  INIT the vCPU to put
+	 * the VMCB in a known good state.  Unfortuately, KVM doesn't have
+	 * KVM_MP_STATE_SHUTDOWN and can't add it without potentially breaking
+	 * userspace.  At a platform view, INIT is acceptable behavior as
+	 * there exist bare metal platforms that automatically INIT the CPU
+	 * in response to shutdown.
 	 */
 	clear_page(svm->vmcb);
-	init_vmcb(vcpu);
+	kvm_vcpu_reset(vcpu, true);
 
 	kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;
 	return 0;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3aa952edd5f4..f35dd8192c32 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10901,6 +10901,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
 	if (init_event)
 		kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
 }
+EXPORT_SYMBOL_GPL(kvm_vcpu_reset);
 
 void kvm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
 {
-- 
2.32.0.93.g670b81a890-goog