The host's decision to enable machine check exceptions should remain
in force during non-root mode. KVM was writing 0 to cr4 on VCPU reset
and passed a slightly-modified 0 to the vmcs.guest_cr4 value.
Tested: Built.
On earlier version, tested by injecting machine check while a guest is spinning.
Before the change, if guest CR4.MCE==0, then the machine check is
escalated to Catastrophic Error (CATERR) and the machine dies.
If guest CR4.MCE==1, then the machine check causes VMEXIT and is
handled normally by host Linux. After the change, injecting a machine
check causes normal Linux machine check handling.
Signed-off-by: Ben Serebrin <serebrin@xxxxxxxxxx>
---
arch/x86/kvm/vmx.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index f5e8dce..f7b6168 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3622,8 +3622,16 @@ static void vmx_set_cr3(struct kvm_vcpu *vcpu,
unsigned long cr3)
static int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
- unsigned long hw_cr4 = cr4 | (to_vmx(vcpu)->rmode.vm86_active ?
- KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON);
+ /*
+ * Pass through host's Machine Check Enable value to hw_cr4, which
+ * is in force while we are in guest mode. Do not let guests control
+ * this bit, even if host CR4.MCE == 0.
+ */
+ unsigned long hw_cr4 =
+ (cr4_read_shadow() & X86_CR4_MCE) |
+ (cr4 & ~X86_CR4_MCE) |
+ (to_vmx(vcpu)->rmode.vm86_active ?
+ KVM_RMODE_VM_CR4_ALWAYS_ON : KVM_PMODE_VM_CR4_ALWAYS_ON);
if (cr4 & X86_CR4_VMXE) {
/*
--
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