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? > > If your code tries to optimize "between VMAs", you really shouldn't be doing > that at this point. No I'm not doing that; It's one VMA at a time. > > If someone did an mprotect(), there are separate VMAs, and you shouldn't be > looking at the PTEs belonging to a different VMA. > Yep understood, thanks.
