On 12/05/2024 18:25, Alexandre Ghiti wrote: > Hi Ryan, > > On Fri, May 10, 2024 at 3:49 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >> >> On 08/05/2024 12:34, Alexandre Ghiti wrote: >>> This patchset intends to merge the contiguous ptes hugetlbfs implementation >>> of arm64 and riscv. >>> >>> Both arm64 and riscv support the use of contiguous ptes to map pages that >>> are larger than the default page table size, respectively called contpte >>> and svnapot. >>> >>> The riscv implementation differs from the arm64's in that the LSBs of the >>> pfn of a svnapot pte are used to store the size of the mapping, allowing >>> for future sizes to be added (for now only 64KB is supported). That's an >>> issue for the core mm code which expects to find the *real* pfn a pte points >>> to. Patch 1 fixes that by always returning svnapot ptes with the real pfn >>> and restores the size of the mapping when it is written to a page table. >>> >>> The following patches are just merges of the 2 different implementations >>> that currently exist in arm64 and riscv which are very similar. It paves >>> the way to the reuse of the recent contpte THP work by Ryan [1] to avoid >>> reimplementing the same in riscv. >> >> Hi Alexandre, >> >> I've skimmed through this series and the one that moves contpte. I can see there >> is definitely value in sharing the implementation, and the rough shape of things >> seems appropriate. I had some minor concerns about making it harder to implement >> potential future arm64 errata workarounds but on reflection, most of the >> now-shared code is really just wrapping the primitives that are still arch-specific. >> >> I'm going to need to spend proper time reviewing it to give detailed feedback, >> but I'll be out on paternity leave for 3 weeks from end of Monday at the latest. > > Too bad, I expected to discuss that with you at LSF/MM...But congrats! > Hope your wife is fine :) Thanks! Yes its unfortunate timing - there are a few topics I would have liked to get involved with. There's always next year... > >> So realistically I won't be able to do the detailed review until at least the >> first week of June. >> >> Some high level thoughts: >> >> - huge_ptep_* functions could be working on different sized huge ptes - arm64 >> supports contpte, pmd, contpmd and pud. Is keeping them in contpte.c >> appropriate? > > Hmm indeed, I'll see what I can do. > >> Perhaps it's better to keep huge_pte and contpte separate? Also, it >> only works on arm64 because we can get away with calling the lower-level pte >> functions even when the huge_pte is actually a contpmd/pmd/pud, because the >> format is the same. That might present challenges to other arches if the format >> is different? > > Yes, but I think that if that happens, we could get away with it by > choosing the right function depending on the size of the mapping? Yes possibly. One potential future new user of this common code would be arm32 (arch/arm), which also has the contig bit. But AIUI, the pmd an pte formats are quite different. It's likely that arm would want to opt-in to contpte but not huge_ptep, so separate selectors may be valuable. > >> >> - It might be easier to review if the arm64 stuff is first moved (without >> changes) then modified to make it suitable for riscv, then for riscv to be >> hooked up. At the moment I'm trying to follow all 3 parts per-function. > > Ok, let me give it a try during your paternity leave! Thanks! If it's too difficult then it's not a deal-breaker. Perhaps just an initial patch to move the existing arm functions to core-mm without change, then all your existing patches on top of that would do the job? > >> >> Thanks, >> Ryan > > Thanks, > > Alex > >> >> >>> >>> This patchset was tested by running the libhugetlbfs testsuite with 64KB >>> and 2MB pages on both architectures (on a 4KB base page size arm64 kernel). >>> >>> [1] https://lore.kernel.org/linux-arm-kernel/20240215103205.2607016-1-ryan.roberts@xxxxxxx/ >>> >>> Changes in v2: >>> - Rebase on top of 6.9-rc3 >>> >>> Alexandre Ghiti (9): >>> riscv: Restore the pfn in a NAPOT pte when manipulated by core mm code >>> riscv: Safely remove huge_pte_offset() when manipulating NAPOT ptes >>> mm: Use common huge_ptep_get() function for riscv/arm64 >>> mm: Use common set_huge_pte_at() function for riscv/arm64 >>> mm: Use common huge_pte_clear() function for riscv/arm64 >>> mm: Use common huge_ptep_get_and_clear() function for riscv/arm64 >>> mm: Use common huge_ptep_set_access_flags() function for riscv/arm64 >>> mm: Use common huge_ptep_set_wrprotect() function for riscv/arm64 >>> mm: Use common huge_ptep_clear_flush() function for riscv/arm64 >>> >>> arch/arm64/Kconfig | 1 + >>> arch/arm64/include/asm/pgtable.h | 56 +++++- >>> arch/arm64/mm/hugetlbpage.c | 291 +--------------------------- >>> arch/riscv/Kconfig | 1 + >>> arch/riscv/include/asm/hugetlb.h | 2 +- >>> arch/riscv/include/asm/pgtable-64.h | 11 ++ >>> arch/riscv/include/asm/pgtable.h | 153 +++++++++++++-- >>> arch/riscv/mm/hugetlbpage.c | 227 ---------------------- >>> arch/riscv/mm/pgtable.c | 6 +- >>> mm/Kconfig | 3 + >>> mm/Makefile | 1 + >>> mm/contpte.c | 272 ++++++++++++++++++++++++++ >>> 12 files changed, 480 insertions(+), 544 deletions(-) >>> create mode 100644 mm/contpte.c >>> >>
