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SubjectRe: [PATCH v1 RESEND 3/6] sparc/mm: don't unconditionally set HW writable bit when setting PTE dirty on 64bit
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>> Let's fix the remaining issues and prepare for reverting the workarounds
>> by setting the HW writable bit only if both, the SW dirty bit and the SW
>> writable bit are set.
>>
>> We have to move pte_dirty() and pte_dirty() up. The code patching
> One of the pte_dirty() should be replaced with pte_write().
>

Indeed, thanks. I assume Andrew can change the latter to pte_write().
[unless I have to resend, of course]

> It would have been nice to separate moving and changes in two patches,
> but keeping it together works too.

I prefer to not have "move code within the same file around" in separate
patches as long as it doesn't add too much noise. Here, I think it's
acceptable.

>
>
>> mechanism and handling constants > 22bit is a bit special on sparc64.
>>
>> The ASM logic in pte_mkdirty() and pte_mkwrite() match the logic in
>> pte_mkold() to create the mask depending on the machine type. The ASM
>> logic in __pte_mkhwwrite() matches the logic in pte_present(), just
>> using an "or" instead of an "and" instruction.
>>
>> With this commit (sun4u in QEMU):
>> root@debian:~/linux/tools/testing/selftests/mm# ./mkdirty
>> # [INFO] detected THP size: 8192 KiB
>> TAP version 13
>> 1..6
>> # [INFO] PTRACE write access
>> ok 1 SIGSEGV generated, page not modified
>> # [INFO] PTRACE write access to THP
>> ok 2 SIGSEGV generated, page not modified
>> # [INFO] Page migration
>> ok 3 SIGSEGV generated, page not modified
>> # [INFO] Page migration of THP
>> ok 4 SIGSEGV generated, page not modified
>> # [INFO] PTE-mapping a THP
>> ok 5 SIGSEGV generated, page not modified
>> # [INFO] UFFDIO_COPY
>> ok 6 SIGSEGV generated, page not modified
>> # Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0
> Nice!
>
>>
>> This handling seems to have been in place forever.
>>
>> [1] https://lkml.kernel.org/r/533a7c3d-3a48-b16b-b421-6e8386e0b142@redhat.com
>>
>> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
>> Signed-off-by: David Hildenbrand <david@redhat.com>
>
> I tried to follow your changes, but my knowledge of gcc assembler failed
> me. But based on the nice and detailed change log and the code I managed
> to understand:
> Acked-by: Sam Ravnborg <sam@ravnborg.org>


Thanks Sam!

--
Thanks,

David / dhildenb

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