Re: [PATCH] KVM: VMX: Preserve host CR4.MCE value while in guest mode.

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Apr 16, 2015 at 11:58:05AM -0700, Ben Serebrin wrote:
> 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>
> ---
>  arch/x86/kvm/vmx.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)

<formletter>

This is not the correct way to submit patches for inclusion in the
stable kernel tree.  Please read Documentation/stable_kernel_rules.txt
for how to do this properly.

</formletter>