Re: [PATCH v1 RESEND 3/6] sparc/mm: don't unconditionally set HW writable bit when setting PTE dirty on 64bit

[David Hildenbrand]

[...]

> > 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@xxxxxxxxxx
> >
> > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
>
> 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@xxxxxxxxxxxx>


Thanks Sam!

--
Thanks,

David / dhildenb