From: Alexandre Ghiti <alexghiti@rivosinc.com>
To: Ryan Roberts <ryan.roberts@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Andrew Morton <akpm@linux-foundation.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
linux-mm@kvack.org
Subject: Re: [PATCH RESEND v2 0/9] Merge arm64/riscv hugetlbfs contpte support
Date: Sun, 12 May 2024 19:25:56 +0200 [thread overview]
Message-ID: <CAHVXubhmihZA50pdaek4=fx83ycdOyuYkRmVLPtZk59uKBoWPw@mail.gmail.com> (raw)
In-Reply-To: <6d37f914-d139-48ea-be63-c428ac767cc1@arm.com>
Hi Ryan,
On Fri, May 10, 2024 at 3:49 PM Ryan Roberts <ryan.roberts@arm.com> 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 :)
> 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?
>
> - 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,
> 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@arm.com/
> >
> > 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
> >
>
next prev parent reply other threads:[~2024-05-12 17:26 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-08 11:34 [PATCH RESEND v2 0/9] Merge arm64/riscv hugetlbfs contpte support Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 1/9] riscv: Restore the pfn in a NAPOT pte when manipulated by core mm code Alexandre Ghiti
2024-05-10 12:20 ` Ryan Roberts
2024-05-13 13:06 ` Alexandre Ghiti
2024-05-13 14:52 ` Ryan Roberts
2024-05-08 11:34 ` [PATCH RESEND v2 2/9] riscv: Safely remove huge_pte_offset() when manipulating NAPOT ptes Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 3/9] mm: Use common huge_ptep_get() function for riscv/arm64 Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 4/9] mm: Use common set_huge_pte_at() " Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 5/9] mm: Use common huge_pte_clear() " Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 6/9] mm: Use common huge_ptep_get_and_clear() " Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 7/9] mm: Use common huge_ptep_set_access_flags() " Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 8/9] mm: Use common huge_ptep_set_wrprotect() " Alexandre Ghiti
2024-05-08 11:34 ` [PATCH RESEND v2 9/9] mm: Use common huge_ptep_clear_flush() " Alexandre Ghiti
2024-05-10 13:49 ` [PATCH RESEND v2 0/9] Merge arm64/riscv hugetlbfs contpte support Ryan Roberts
2024-05-12 17:25 ` Alexandre Ghiti [this message]
2024-05-13 8:59 ` Ryan Roberts
2024-05-28 8:07 ` Alexandre Ghiti
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