linux-kernel - [PATCH AUTOSEL for 4.14 006/100] KVM: nVMX/nSVM: Don't intercept #UD when running L2

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Message-ID: <20180124041414.32065-6-alexander.levin@microsoft.com>
Date:   Wed, 24 Jan 2018 04:14:24 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
CC:     Liran Alon <liran.alon@...cle.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL for 4.14 006/100] KVM: nVMX/nSVM: Don't intercept #UD
 when running L2

From: Liran Alon <liran.alon@...cle.com>

[ Upstream commit ac9b305caa0df6f5b75d294e4b86c1027648991e ]

When running L2, #UD should be intercepted by L1 or just forwarded
directly to L2. It should not reach L0 x86 emulator.
Therefore, set intercept for #UD only based on L1 exception-bitmap.

Also add WARN_ON_ONCE() on L0 #UD intercept handlers to make sure
it is never reached while running L2.

This improves commit ae1f57670703 ("KVM: nVMX: Do not emulate #UD while
in guest mode") by removing an unnecessary exit from L2 to L0 on #UD
when L1 doesn't intercept it.

In addition, SVM L0 #UD intercept handler doesn't handle correctly the
case it is raised from L2. In this case, it should forward the #UD to
guest instead of x86 emulator. As done in VMX #UD intercept handler.
This commit fixes this issue as-well.

Signed-off-by: Liran Alon <liran.alon@...cle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@...cle.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Reviewed-by: Paolo Bonzini <pbonzini@...hat.com>
Reviewed-by: Wanpeng Li <wanpeng.li@...mail.com>
Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 arch/x86/kvm/svm.c | 9 ++++++++-
 arch/x86/kvm/vmx.c | 9 ++++-----
 2 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 6a8284f72328..c8be4e6d365b 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -362,6 +362,7 @@ static void recalc_intercepts(struct vcpu_svm *svm)
 {
 	struct vmcb_control_area *c, *h;
 	struct nested_state *g;
+	u32 h_intercept_exceptions;
 
 	mark_dirty(svm->vmcb, VMCB_INTERCEPTS);
 
@@ -372,9 +373,14 @@ static void recalc_intercepts(struct vcpu_svm *svm)
 	h = &svm->nested.hsave->control;
 	g = &svm->nested;
 
+	/* No need to intercept #UD if L1 doesn't intercept it */
+	h_intercept_exceptions =
+		h->intercept_exceptions & ~(1U << UD_VECTOR);
+
 	c->intercept_cr = h->intercept_cr | g->intercept_cr;
 	c->intercept_dr = h->intercept_dr | g->intercept_dr;
-	c->intercept_exceptions = h->intercept_exceptions | g->intercept_exceptions;
+	c->intercept_exceptions =
+		h_intercept_exceptions | g->intercept_exceptions;
 	c->intercept = h->intercept | g->intercept;
 }
 
@@ -2189,6 +2195,7 @@ static int ud_interception(struct vcpu_svm *svm)
 {
 	int er;
 
+	WARN_ON_ONCE(is_guest_mode(&svm->vcpu));
 	er = emulate_instruction(&svm->vcpu, EMULTYPE_TRAP_UD);
 	if (er == EMULATE_USER_EXIT)
 		return 0;
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ef16cf0f7cfd..36628ed362d8 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1891,7 +1891,7 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
 {
 	u32 eb;
 
-	eb = (1u << PF_VECTOR) | (1u << UD_VECTOR) | (1u << MC_VECTOR) |
+	eb = (1u << PF_VECTOR) | (1u << MC_VECTOR) |
 	     (1u << DB_VECTOR) | (1u << AC_VECTOR);
 	if ((vcpu->guest_debug &
 	     (KVM_GUESTDBG_ENABLE | KVM_GUESTDBG_USE_SW_BP)) ==
@@ -1909,6 +1909,8 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
 	 */
 	if (is_guest_mode(vcpu))
 		eb |= get_vmcs12(vcpu)->exception_bitmap;
+	else
+		eb |= 1u << UD_VECTOR;
 
 	vmcs_write32(EXCEPTION_BITMAP, eb);
 }
@@ -5919,10 +5921,7 @@ static int handle_exception(struct kvm_vcpu *vcpu)
 		return 1;  /* already handled by vmx_vcpu_run() */
 
 	if (is_invalid_opcode(intr_info)) {
-		if (is_guest_mode(vcpu)) {
-			kvm_queue_exception(vcpu, UD_VECTOR);
-			return 1;
-		}
+		WARN_ON_ONCE(is_guest_mode(vcpu));
 		er = emulate_instruction(vcpu, EMULTYPE_TRAP_UD);
 		if (er == EMULATE_USER_EXIT)
 			return 0;
-- 
2.11.0