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

[Linus Torvalds]

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.

We do something very similar for the old Pentium F0 0F bug - we mark
the IDT read-only, which causes the (bogus) locked read of the IDT
entry that the F00F bug resulted in to be caught as a page fault
instead.

              Linus
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