Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1495180

Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch to userspace

Show all headers | View raw

On Mon, Oct 3, 2016 at 7:47 PM, Rik van Riel <riel@redhat.com> wrote:
> On Mon, 2016-10-03 at 19:09 -0700, Andy Lutomirski wrote:
>
>> > Having two separate status booleans for "registers valid"
>> > and "memory valid" may make more sense.
>>
>> I have no problem with the concept of "owner_ctx", and I think it's a
>> perfectly reasonable data structure.  My problem with it is that it's
>> subtle and knowledge of it is spread all over the place.  Just going
>> with "registers valid" in a variable won't work, I think, because
>> there's nowhere to put it.  We need to be able to delete a struct fpu
>> while that struct fpu might have a valid copy in a different cpu's
>> registers.
>>
>> Anyway, feel free to tell me that I'm making this too difficult :)
>
> How about we rename fpu_want_lazy_restore to
> fpu_registers_valid()?  Problem solved :)
>
> Then we can rename __cpu_disable_lazy_restore
> to fpu_invalidate_registers(), and call that
> before we modify any in-memory FPU state.

Sounds good to me.

>
>> > We can get rid of fpu.counter, since nobody uses it
>> > any more.
>>
>> We should definitely do this.
>>
>> Maybe getting in some cleanups first (my lazy fpu deletion,
>> fpu.counter removal, etc) first is the way to go.
>
> Sounds good.  I will keep my patch 1/4 as part of the
> cleanup series, and will not move on to the harder
> stuff until after the cleanups.
>
> Any other stuff I should clean up while we're there?

Almost certainly, but nothing I'm thinking of right now :)

>
>> > > > >
>> > You are right, read_pkru() and write_pkru() can only deal with
>> > the pkru state being present in registers. Is this because of an
>> > assumption in the code, or because of a hardware requirement?
>
> read_pkru and write_pkru would be candidates for using
> fpu_registers_valid, and potentially a fpu_make_registers_valid,
> which restores the contents of the fpu registers from memory,
> if fpu_registers_valid is not true.
>
> Likewise, we can have an fpu_make_memory_valid to ensure the
> in kernel memory copy of the FPU registers is valid, potentially
> a _read and _write version that do exactly what the pstate code
> wants today.
>
> Would that make sense as an API?
>
> --
> All Rights Reversed.



-- 
Andy Lutomirski
AMA Capital Management, LLC

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

[PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch to userspace riel@redhat.com - 2016-10-01 23:00 +0200
  Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Andy Lutomirski <luto@amacapital.net> - 2016-10-02 01:50 +0200
    Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-02 02:10 +0200
      Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Andy Lutomirski <luto@amacapital.net> - 2016-10-03 23:00 +0200
        Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-03 23:30 +0200
          Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Andy Lutomirski <luto@amacapital.net> - 2016-10-03 23:40 +0200
            Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-04 03:30 +0200
              Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Andy Lutomirski <luto@amacapital.net> - 2016-10-04 04:20 +0200
                Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-04 04:50 +0200
                Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Andy Lutomirski <luto@amacapital.net> - 2016-10-04 05:10 +0200
                Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Ingo Molnar <mingo@kernel.org> - 2016-10-04 08:40 +0200
                Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-04 14:50 +0200
            Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-04 04:20 +0200
              Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Andy Lutomirski <luto@amacapital.net> - 2016-10-04 05:10 +0200
    Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until  switch to userspace Rik van Riel <riel@redhat.com> - 2016-10-02 02:50 +0200
      Re: [PATCH RFC 2/5] x86,fpu: delay FPU register loading until switch  to userspace Dave Hansen <dave.hansen@linux.intel.com> - 2016-10-03 18:30 +0200

csiph-web