lkml.org 
[lkml]   [2021]   [Jun]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] x86/cpufeatures: Force disable X86_FEATURE_ENQCMD and remove update_pasid()
From
Date
On 6/2/21 1:37 PM, Luck, Tony wrote:
>>> ... so on a PASID system, your trivial reproducer would theoretically
>>> fire the same way and corrupt FPU state just as well.
>>
>> This is worse and you can't selftest it because the IPI can just hit in
>> the middle of _any_ FPU state operation and corrupt state.
>
> That sounds like we should abandon the "IPI all the other threads
> to force enable the PASID for them" approach. It would just be a
> nightmare of papering over cracks when the IPI was delivered at
> some inconvenient moment when the recipient was in the middle
> of touching xsave state.
>
> I've told Fenghua to dig out the previous iteration of this patch where
> the plan was to lazily fix the PASID_MSR in other threads in the #GP
> handler.

Blech. Also this won't work for other PASID-like features.

I have a half-written patch to fix this up for real. Stay tuned.

> Seems like a better direction than trying to fix the IPI method. The virtualization
> folks will like this way more because IPI in guest causes a couple of VMEXIT
> so is somewhat expensive.

It happens at most once per PASID-using process.

\
 
 \ /
  Last update: 2021-06-03 19:31    [W:0.083 / U:0.928 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site