Re: KVM: nSVM: Check for NRIPS support before updating control field

[Bandan Das <bsd@redhat.com>]

Greg KH <gregkh@linuxfoundation.org> writes:

> On Mon, Jun 29, 2015 at 03:18:51PM -0400, Bandan Das wrote:
>> 
>> Commit f104765b4f81fd74d69e0eb161e89096deade2db upstream.
>> 
>> This causes the L1 guest to crash when running a nested guest
>> with an AMD processor that doesn't support NRIPS.
>> 
>> If hardware doesn't support DecodeAssist - a feature that provides
>> more information about the intercept in the VMCB, KVM decodes the
>> instruction and then updates the next_rip vmcb control field.
>> However, NRIP support itself depends on cpuid Fn8000_000A_EDX[NRIPS].
>> Since skip_emulated_instruction() doesn't verify nrip support
>> before accepting control.next_rip as valid, avoid writing this
>> field if support isn't present.
>> 
>> Signed-off-by: Bandan Das <bsd@redhat.com>
>> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
>> ---
>>  arch/x86/kvm/svm.c | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>
> What stable kernel trees do you want this applied to?

Sorry, I missed that part. I believe this bug is present
since commit cfec82cb7d3 which makes it applicable to
#3.0+

Bandan
> thanks,
>
> greg k-h