> 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. 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.
