Re: Updated version of RD/WR FS/GS BASE patchkit

From	Andi Kleen <andi@firstfloor.org>
Newsgroups	linux.kernel
Subject	Re: Updated version of RD/WR FS/GS BASE patchkit
Date	2016-03-21 23:20 +0100
Message-ID	<rfgl4-3uK-21@gated-at.bofh.it> (permalink)
References	(1 earlier) <rfdGy-1FG-23@gated-at.bofh.it> <rfdGy-1FG-25@gated-at.bofh.it> <rfdGy-1FG-21@gated-at.bofh.it> <rfdZU-1O7-9@gated-at.bofh.it> <rfgbn-3qY-5@gated-at.bofh.it>
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> So a patchset to enable these asinine new instructions needs to take
> this into account, and the ABI issue needs to be addressed, even if

What's the ABI issue?

AFAIK we're perfectly consistent.

> the answer is that the proposed code is fine.
> 
> (Also, the existing code is fscked up.  Guess what xor %eax, %eax; mov
> %ax, %gs does to the base on AMD?  The existing code is *wrong*, and I
> don't want to see it get wronger.)

I have no idea, but changing it is definitely not in scope for my patches.

> 
> And no, I don't really care about programs detecting context switches.
> I do, however, care about allowing non-determinism in things that
> ought to behave deterministically.  Writing a nonzero value to %gs and
> then doing WRGSBASE is something that user code will be able to do
> whether we like it or not, some shitty threading library is likely to
> do this just to spite us, the the kernel needs to do *something* when
> this happens.

They will quickly notice it if there is a problem, so I don't think
we need to worry about that.

-Andi

-- 
ak@linux.intel.com -- Speaking for myself only.

Thread

Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-21 17:20 +0100
  Re: Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski <luto@amacapital.net> - 2016-03-21 20:30 +0100
    Re: Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-21 20:50 +0100
      Re: Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski <luto@amacapital.net> - 2016-03-21 23:10 +0100
        Re: Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-21 23:20 +0100
          Re: Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski <luto@amacapital.net> - 2016-03-21 23:30 +0100
            Re: Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-21 23:50 +0100
              Re: Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski <luto@amacapital.net> - 2016-03-21 23:50 +0100
                Re: Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski <luto@amacapital.net> - 2016-03-22 00:00 +0100
                Re: Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-22 00:10 +0100
                Re: Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-22 00:00 +0100
  Re: Updated version of RD/WR FS/GS BASE patchkit Andi Kleen <andi@firstfloor.org> - 2016-03-21 20:30 +0100
  Re: Updated version of RD/WR FS/GS BASE patchkit Andy Lutomirski <luto@amacapital.net> - 2016-03-21 20:50 +0100

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