Re: [PATCH] x86: Use entire page for the per-cpu GDT only if paravirt-enabled

From: H. Peter Anvin
Date: Tue Sep 29 2015 - 16:31:56 EST

On 09/29/2015 11:02 AM, Andy Lutomirski wrote:
> On Tue, Sep 29, 2015 at 10:50 AM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> On Tue, Sep 29, 2015 at 1:35 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>> Does anyone know what happens if you stick a non-accessed segment in
>>> the GDT, map the GDT RO, and access it?
>> You should get a #PF, as you guess, but go ahead and test it if you
>> want to make sure.
> Then I think that, if we do this, the patch series should first make
> it percpu and fixmapped but RW and then flip it RO as a separate patch
> in case we need to revert the actual RO bit. I don't want to break
> Wine or The Witcher 2 because of this, and we might need various
> fixups. I really hope that no one uses get_thread_area to check
> whether TLS has been accessed.

Of course.


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