[PATCH 0/3] SVM: handle MCEs properly

[PATCH 0/3] SVM: handle MCEs properly

[Joerg Roedel]

This patchset implements proper MCE handling for SVM in the KVM hypervisor.
Currently KVM does not set CR4.MCE when it runs the guest. When a MCE condition
occurs while the guest is running the exception gets lost. This may result in
data corruption or other undefined behaviour. This patchset sets CR4.MCE to the
value in the host and adds the intercept for machine check exceptions to the
SVM implementation. When this intercept occurs, it calls the host MCE exception
handler manually.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>




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[PATCH 1/3] SVM: indent svm_set_cr4 with tabs instead of spaces

[Joerg Roedel]

The smv_set_cr4 function is indented with spaces. This patch replaces them with
tabs.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 arch/x86/kvm/svm.c |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index ad27346..d7439ce 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -878,10 +878,10 @@ set:
 
 static void svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
-       vcpu->arch.cr4 = cr4;
-       if (!npt_enabled)
-	       cr4 |= X86_CR4_PAE;
-       to_svm(vcpu)->vmcb->save.cr4 = cr4;
+	vcpu->arch.cr4 = cr4;
+	if (!npt_enabled)
+		cr4 |= X86_CR4_PAE;
+	to_svm(vcpu)->vmcb->save.cr4 = cr4;
 }
 
 static void svm_set_segment(struct kvm_vcpu *vcpu,
-- 
1.5.3.7



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[PATCH 2/3] SVM: align shadow CR4.MCE with host

[Joerg Roedel]

This patch aligns the host version of the CR4.MCE bit with the CR4 active in
the guest. This is necessary to get MCE exceptions when the guest is running.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 arch/x86/kvm/svm.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d7439ce..8af463b 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -878,9 +878,12 @@ set:
 
 static void svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 {
+	unsigned long host_cr4_mce = read_cr4() & X86_CR4_MCE;
+
 	vcpu->arch.cr4 = cr4;
 	if (!npt_enabled)
 		cr4 |= X86_CR4_PAE;
+	cr4 |= host_cr4_mce;
 	to_svm(vcpu)->vmcb->save.cr4 = cr4;
 }
 
-- 
1.5.3.7



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[PATCH 3/3] SVM: add intercept for machine check exception

[Joerg Roedel]

To properly forward a MCE occured while the guest is running to the host, we
have to intercept this exception and call the host handler by hand. This is
implemented by this patch.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
---
 arch/x86/kvm/svm.c         |   17 ++++++++++++++++-
 include/asm-x86/kvm_host.h |    1 +
 2 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 8af463b..da3ddef 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -507,7 +507,8 @@ static void init_vmcb(struct vcpu_svm *svm)
 					INTERCEPT_DR7_MASK;
 
 	control->intercept_exceptions = (1 << PF_VECTOR) |
-					(1 << UD_VECTOR);
+					(1 << UD_VECTOR) |
+					(1 << MC_VECTOR);
 
 
 	control->intercept = 	(1ULL << INTERCEPT_INTR) |
@@ -1044,6 +1045,19 @@ static int nm_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 	return 1;
 }
 
+static int mc_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
+{
+	/*
+	 * On an #MC intercept the MCE handler is not called automatically in
+	 * the host. So do it by hand here.
+	 */
+	asm volatile (
+		"int $0x12\n");
+	/* not sure if we ever come back to this point */
+
+	return 1;
+}
+
 static int shutdown_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)
 {
 	/*
@@ -1367,6 +1381,7 @@ static int (*svm_exit_handlers[])(struct vcpu_svm *svm,
 	[SVM_EXIT_EXCP_BASE + UD_VECTOR]	= ud_interception,
 	[SVM_EXIT_EXCP_BASE + PF_VECTOR] 	= pf_interception,
 	[SVM_EXIT_EXCP_BASE + NM_VECTOR] 	= nm_interception,
+	[SVM_EXIT_EXCP_BASE + MC_VECTOR] 	= mc_interception,
 	[SVM_EXIT_INTR] 			= nop_on_interception,
 	[SVM_EXIT_NMI]				= nop_on_interception,
 	[SVM_EXIT_SMI]				= nop_on_interception,
diff --git a/include/asm-x86/kvm_host.h b/include/asm-x86/kvm_host.h
index 781fc87..551ff1d 100644
--- a/include/asm-x86/kvm_host.h
+++ b/include/asm-x86/kvm_host.h
@@ -61,6 +61,7 @@
 #define SS_VECTOR 12
 #define GP_VECTOR 13
 #define PF_VECTOR 14
+#define MC_VECTOR 18
 
 #define SELECTOR_TI_MASK (1 << 2)
 #define SELECTOR_RPL_MASK 0x03
-- 
1.5.3.7



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Re: [PATCH 0/3] SVM: handle MCEs properly

[Avi Kivity]

Joerg Roedel wrote:
> This patchset implements proper MCE handling for SVM in the KVM hypervisor.
> Currently KVM does not set CR4.MCE when it runs the guest. When a MCE condition
> occurs while the guest is running the exception gets lost. This may result in
> data corruption or other undefined behaviour. This patchset sets CR4.MCE to the
> value in the host and adds the intercept for machine check exceptions to the
> SVM implementation. When this intercept occurs, it calls the host MCE exception
> handler manually.
>
>   

Applied all, thanks.

-- 
Any sufficiently difficult bug is indistinguishable from a feature.


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