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[Xen-devel] Re: [PATCH] Fix performance problems with mprotect()

I'm not sure how this BUG_ON would get triggered with current x86 paging 
semantics, and probably isn't needed I think.
Am I missing something?
The code is almost exactly the same as the existing update_intpte, which has 
the same BUG_ON, and so I just left it in.
(BTW:I considered merging the new functions into the non "sync" versions but 
opted not to.)

- Bruce

>>> On 1/7/2008 at 8:18 AM, in message <p73d4sdsly4.fsf@xxxxxxxxxxxxxx>, Andi 
>>> Kleen
<andi@xxxxxxxxxxxxxx> wrote:
> "Bruce Rogers" <brogers@xxxxxxxxxx> writes:
>> +
>> +        /* Allowed to change in Accessed/Dirty flags only. */
>> +        BUG_ON((t ^ old) & ~(intpte_t)(_PAGE_ACCESSED|_PAGE_DIRTY));
> Are you sure that BUG_ON can't be triggered from the hypercall?
> It should error out in this case I think.
> -Andi

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