On Sun, 2018-08-26 at 07:18 -0700, Andy Lutomirski wrote: > > On Aug 26, 2018, at 7:06 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> > > wrote: > > > > Jason, > > > > > On Sun, 26 Aug 2018, Jason A. Donenfeld wrote: > > > > On Sun, Aug 26, 2018 at 6:10 AM Thomas Gleixner < > > > > tglx@xxxxxxxxxxxxx> wrote: > > > > I'm not too fond of this simply because it requires that > > > > relax() step in > > > > all code pathes. I'd rather make that completely transparent by > > > > just > > > > marking the task as FPU using and let the context switch code > > > > deal with it > > > > in case that it gets preempted. I'll let one of my engineers > > > > look into > > > > that next week. > > > > > > Do you mean to say you intend to make kernel_fpu_end() and > > > kernel_neon_end() only actually do something upon context switch, > > > but > > > not when it's actually called? So that multiple calls to > > > kernel_fpu_begin() and kernel_neon_begin() can be made without > > > penalty? > > > > On context switch and exit to user. That allows to keep those code > > pathes > > fully preemptible. Still twisting my brain around the details. > > I think you’ll have to treat exit to user and context switch as > different things. For exit to user, we want to restore the *user* > state, but, for context switch, we’ll need to restore *kernel* state. For non-preemptible kernel_fpu_begin/end (which seems like a good starting point since since it gets the code halfway to where Thomas would like it to go), the rules would be a little simpler: - For exit to userspace, restore the user FPU state. - At kernel_fpu_begin(), save the user FPU state (if still loaded). - At context switch time, save the user FPU state (if still loaded). > Do user first as its own patch set. It’ll be less painful that way. > > And someone needs to rework PKRU for this to make sense. See previous > threads. I sent Thomas the patches I worked on in the past. That series is likely incomplete, but should be a reasonable starting point. -- All Rights Reversed.
Attachment:
signature.asc
Description: This is a digitally signed message part
