Re: [PATCH v2 12/12] x86/traps: Fix up invalid PASID

[Andy Lutomirski]

> On Jun 15, 2020, at 1:56 PM, Luck, Tony <tony.l...@intel.com> wrote:
> 
> 
>> 
>> Are we planning to keep PASID live once a task has used it once or are we 
>> going to swap it lazily?  If the latter, a percpu variable might be better.
> 
> Current plan is "touch it once and the task owns it until exit(2)"
> 
> Maybe someday in the future when we have data on how applications
> actually use accelerators we could look at something more complex
> if usage patterns look like it would be beneficial.
> 
> 

So what’s the RDMSR for?  Surely you
have some state somewhere that says “this task has a PASID.”  Can’t you just 
make sure that stays in sync with the MSR?  Then, on #GP, if the task already 
has a PASID, you know the MSR is set.