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We used to have624a2c94f5(Partly revert "mm/thp: carry over dirty bit when thp splits on pmd") fixing the regression reported here by Anatoly Pugachev on sparc64: https://lore.kernel.org/r/20221021160603.GA23307@u164.east.ru Where we temporarily ignored the dirty bit for small pages. Then, Hev also reported similar issue on loongarch: (the original mail was private, but Anatoly copied the list here) https://lore.kernel.org/r/CADxRZqxqb7f_WhMh=jweZP+ynf_JwGd-0VwbYgp4P+T0-AXosw@mail.gmail.com Hev pointed out that the issue is having HW write bit set within the pte_mkdirty() so the split pte can be written after split even if e.g. they were shared by more than one processes, causing data corrupt. Hev also tried to explain why loongarch set HW write bit in mkdirty: https://lore.kernel.org/r/CAHirt9itKO_K_HPboXh5AyJtt16Zf0cD73PtHvM=na39u_ztxA@mail.gmail.com One way to fix it is as what Huacai proposed here for loongarch (then we can re-apply the dirty bit in thp split): https://lore.kernel.org/r/20221117042532.4064448-1-chenhuacai@loongson.cnn We may need similar thing for sparc64, though. For now since we've found the root cause of the dirty bit issue the simpler solution (which won't lose the dirty bit for small) that will work for both is we wr-protect after pte_mkdirty(), so the HW write bit can be persistent after thp split. Add a comment for wrprotect, so we will not mess up the ordering later. With624a2c94f5(Partly revert "mm/thp: carry over dirty bit when thp splits on pmd") this is not a fix anymore, but just brings back the dirty bit for thp split safely, so we re-apply the optimization but in safe way. Provide a Tested-by credit to Hev too (not the exact same patch but the same outcome) for loongarch. Link: https://lkml.kernel.org/r/20221125185857.3110155-1-peterx@redhat.com Signed-off-by: Peter Xu <peterx@redhat.com> Tested-by: Hev <r@hev.cc> # loongarch Cc: Anatoly Pugachev <matorola@gmail.com> Cc: Raghavendra K T <raghavendra.kt@amd.com> Cc: Thorsten Leemhuis <regressions@leemhuis.info> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.