Re: [Xen-devel] using PageForeign for pte allocation vs. shortcutting __pte_free_tlb()

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

>>> Gerd Hoffmann <kraxel@xxxxxxx> 09.01.07 12:11 >>>
>Jan Beulich wrote:
>>>>> Gerd Hoffmann <kraxel@xxxxxxx> 09.01.07 11:51 >>>
>>> Jan Beulich wrote:
>>>> In the course of trying to get CONFIG_HIGHPTE to work I stumbled across 
>>>> this
>>>> inconsistency between i386 and x86-64 Linux: i386 uses SetPageForeign() in
>>>> (one the non-highpte) case of pte_alloc_one(), and leaves intact native's
>>>> definition of __pte_free_tlb(), whereas x86-64 doesn't use the former but
>>>> shortcuts the latter to just invoke pte_free(). Obviously it would be nice 
>>>> for
>>>> these two to be consistent,
>>> x86-64 has no HIGHMEM zone, thus CONFIG_HIGHPTE has no effect (I'm
>>> surprised it exists in the first place ...).
>> 
>> Of course (and no, such a config option doesn't exist for x86-64), but what
>> relation does this have to the question asked?
>
>guess (not having looked at the code at all) i386 does that because it
>needs disturgish high and non-high ptes, whereas x86-64 simply has no
>need for that, so I don't see the point in trying to make them
>consistent ...

I'm pretty sure that's not the reason, partly because CONFIG_HIGHPTE (as
indicated here and earlier) isn't being an option for Xen kernels so far at all,
but mostly because as I understand it both mechanisms are ways to
remove the write protection before handing a former page table page back
to the page allocator (and this requirement is clearly the same on both i386
and x86-64).

Jan

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