Commit 085e68ee authored Apr 16, 2015 by Ben Serebrin Committed by Paolo Bonzini Apr 21, 2015

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>

parent decf6333

arch/x86/kvm/vmx.c

+10 −2

Original line number	Diff line number	Diff line
		@@ -3622,7 +3622,15 @@ 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 ?
		/*
		* 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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