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KVM: VMX: Preserve host CR4.MCE value while in guest mode. 

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@google.com>
Reviewed-by: Venkatesh Srinivas <venkateshs@google.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Ben Serebrin 2015-04-16 11:58:05 -07:00 committed by Paolo Bonzini
parent decf63336e
commit 085e68eeaf
1 changed files with 10 additions and 2 deletions
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12
arch/x86/kvm/vmx.c
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@ -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) {
/*