On 16.11.23 11:36, Ryan Roberts wrote:
On 16/11/2023 10:12, David Hildenbrand wrote:
On 16.11.23 11:07, Ryan Roberts wrote:
Hi All,
Hoping for some guidance below!
On 15/11/2023 21:26, kernel test robot wrote:
Hi Ryan,
kernel test robot noticed the following build errors:
[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on linus/master v6.7-rc1 next-20231115]
[cannot apply to arm64/for-next/core efi/next]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]
url:
https://github.com/intel-lab-lkp/linux/commits/Ryan-Roberts/mm-Batch-copy-PTE-ranges-during-fork/20231116-010123
base: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git
mm-everything
patch link:
https://lore.kernel.org/r/20231115163018.1303287-2-ryan.roberts%40arm.com
patch subject: [PATCH v2 01/14] mm: Batch-copy PTE ranges during fork()
config: arm-randconfig-002-20231116
(https://download.01.org/0day-ci/archive/20231116/202311160516.kHhfmjvl-lkp@xxxxxxxxx/config)
compiler: arm-linux-gnueabi-gcc (GCC) 13.2.0
reproduce (this is a W=1 build):
(https://download.01.org/0day-ci/archive/20231116/202311160516.kHhfmjvl-lkp@xxxxxxxxx/reproduce)
If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@xxxxxxxxx>
| Closes:
https://lore.kernel.org/oe-kbuild-all/202311160516.kHhfmjvl-lkp@xxxxxxxxx/
All errors (new ones prefixed by >>):
mm/memory.c: In function 'folio_nr_pages_cont_mapped':
mm/memory.c:969:16: error: implicit declaration of function 'pte_pgprot';
did you mean 'ptep_get'? [-Werror=implicit-function-declaration]
969 | prot = pte_pgprot(pte_mkold(pte_mkclean(ptent)));
| ^~~~~~~~~~
| ptep_get
cc1: some warnings being treated as errors
It turns out that pte_pgprot() is not universal; its only implemented by
architectures that select CONFIG_HAVE_IOREMAP_PROT (currently arc, arm64,
loongarch, mips, powerpc, s390, sh, x86).
I'm using it in core-mm to help calculate the number of "contiguously mapped"
pages within a folio (note that's not the same as arm64's notion of
contpte-mapped. I just want to know that there are N physically contiguous pages
mapped virtually contiguously with the same permissions). And I'm using
pte_pgprot() to extract the permissions for each pte to compare. It's important
that we compare the permissions because just because the pages belongs to the
same folio doesn't imply they are mapped with the same permissions; think
mprotect()ing a sub-range.
I don't have a great idea for how to fix this - does anyone have any thoughts?
KIS :) fork() operates on individual VMAs if I am not daydreaming.
Just check for the obvious pte_write()/dirty/ and you'll be fine.
Yes, that seems much simpler! I think we might have to be careful about the uffd
wp bit too? I think that's it - are there any other exotic bits that might need
to be considered?
Good question. Mimicing what the current code already does should be
sufficient. uffd-wp should have the PTE R/O. You can set the contpte bit
independent of any SW bit (uffd-wp, softdirty, ...) I guess, no need to
worry about that.
--
Cheers,
David / dhildenb
