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

[Andy Lutomirski]

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.

--Andy
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