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Re: [Xen-devel] [PATCH] x86: make IDT read-only

On 04/10/2013 09:31 AM, Eric Northup wrote:
>> If the effect is measurable I agree it is a legitimate optimization.  At
>> one point there was a suggestion to make the code in the IDT vectors
>> differ based on the which interrupt was registed.  While that can also
>> reduce cache misses that can get hairy very quickly, and of course that
>> would require read-write IDTs.
> read-write IDT or GDT are fine: map them twice, once read+write, once
> read-only.  Point the GDTR and IDTR at the read-only alias.

Well, it is weaker, because if you can discover the pointer to the
writable alias you win.

Now, as has been pointed out the GDT needs to be writable on 32 bits as
a matter of hardware requirement.  However, doing it for 64 bits only is
probably enough of a win.


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