> On Aug 20, 2020, at 1:15 PM, Tom Lendacky <thomas.lenda...@amd.com> wrote:
>
> On 8/20/20 3:07 PM, Dave Hansen wrote:
>> On 8/20/20 12:05 PM, Tom Lendacky wrote:
>>>> I added a quick hack to save TSC_AUX to a new variable in the SVM
>>>> struct and then restore it right after VMEXIT (just after where GS is
>>>> restored in svm_vcpu_enter_exit()) and my guest is no longer crashing.
>>>
>>> Sorry, I mean my host is no longer crashing.
>> Just to make sure I've got this:
>> 1. Older CPUs didn't have X86_FEATURE_RDPID
>> 2. FSGSBASE patches started using RDPID in the NMI entry path when
>> supported *AND* FSGSBASE was enabled
>> 3. There was a latent SVM bug which did not restore the RDPID data
>> before NMIs were reenabled after VMEXIT
>> 4. If an NMI comes in the window between VMEXIT and the
>> wrmsr(TSC_AUX)... boom
>
> Right, which means that the setting of TSC_AUX to the guest value needs to be
> moved, too.
>
Depending on how much of a perf hit this is, we could also skip using RDPID in
the paranoid path on SVM-capable CPUs.
