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SubjectRe: [PATCH 16 of 55] xen64: add extra pv_mmu_ops
Mark McLoughlin wrote:
> Hey Jeremy,
>
> On Tue, 2008-07-08 at 15:06 -0700, Jeremy Fitzhardinge wrote:
>
>> We need extra pv_mmu_ops for 64-bit, to deal with the extra level of
>> pagetable.
>>
>> Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
>> ---
>> arch/x86/xen/enlighten.c | 33 +++++++++++++++++++++++++++-
>> arch/x86/xen/mmu.c | 51 +++++++++++++++++++++++++++++++++++++++++++-
>> arch/x86/xen/mmu.h | 15 +++++++++++-
>> include/asm-x86/xen/page.h | 4 +++
>> 4 files changed, 99 insertions(+), 4 deletions(-)
>>
> ...
>
>> diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
>> --- a/arch/x86/xen/mmu.c
>> +++ b/arch/x86/xen/mmu.c
>> @@ -438,14 +438,19 @@
>>
>> void xen_set_pte(pte_t *ptep, pte_t pte)
>> {
>> +#ifdef CONFIG_X86_PAE
>> ptep->pte_high = pte.pte_high;
>> smp_wmb();
>> ptep->pte_low = pte.pte_low;
>> +#else
>> + *ptep = pte;
>> +#endif
>> }
>>
>
> You've dropped non-PAE support already, right? Any reason to use the
> X86_PAE macro instead of X86_32?
>

It's a fine difference, but the specific thing I'm testing for is
actually PAE vs 64-bit (or even more specifically "can I update a whole
pte atomically?"). Testing for X86_32 is equivalent in the absence of
non-PAE 32-bit, but not quite as correct. The other way I could do it
is as I have elsewhere:

if (sizeof(pte_t) > sizeof(long)) {
ptep->pte_high = pte.pte_high;
smp_wmb();
ptep->pte_low = pte.pte_low;
} else
*ptep = pte;

But there are other places where it tests for this using PAE (and even
whole pvops which are only defined in the PAE case).

You'll notice other places where I test for PAGETABLE_LEVELS == 3 where
the code is generally handling 3-level pagetables, and others where I
test for PAE where it's something specific to PAE.

J


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