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Message-ID: <b994ff89-1a1f-26ca-9479-b08c77f94be8@arm.com>
Date: Mon, 3 Jul 2023 10:48:27 +0100
From: Ryan Roberts <ryan.roberts@....com>
To: John Hubbard <jhubbard@...dia.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Ard Biesheuvel <ardb@...nel.org>,
Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>,
James Morse <james.morse@....com>,
Suzuki K Poulose <suzuki.poulose@....com>,
Zenghui Yu <yuzenghui@...wei.com>,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Alexander Potapenko <glider@...gle.com>,
Andrey Konovalov <andreyknvl@...il.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Anshuman Khandual <anshuman.khandual@....com>,
Matthew Wilcox <willy@...radead.org>,
Yu Zhao <yuzhao@...gle.com>,
Mark Rutland <mark.rutland@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-mm@...ck.org
Subject: Re: [PATCH v1 11/14] arm64/mm: Wire up PTE_CONT for user mappings
On 30/06/2023 02:54, John Hubbard wrote:
> On 6/22/23 07:42, Ryan Roberts wrote:
>> With the ptep API sufficiently refactored, we can now introduce a new
>> "contpte" API layer, which transparently manages the PTE_CONT bit for
>> user mappings. Whenever it detects a set of PTEs that meet the
>> requirements for a contiguous range, the PTEs are re-painted with the
>> PTE_CONT bit.
>>
>> This initial change provides a baseline that can be optimized in future
>> commits. That said, fold/unfold operations (which imply tlb
>> invalidation) are avoided where possible with a few tricks for
>> access/dirty bit management.
>>
>> Write-enable and write-protect modifications are likely non-optimal and
>> likely incure a regression in fork() performance. This will be addressed
>> separately.
>>
>> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
>> ---
>
> Hi Ryan!
>
> While trying out the full series from your gitlab features/granule_perf/all
> branch, I found it necessary to EXPORT a symbol in order to build this.
Thanks for the bug report!
> Please see below:
>
> ...
>> +
>> +pte_t contpte_ptep_get(pte_t *ptep, pte_t orig_pte)
>> +{
>> + /*
>> + * Gather access/dirty bits, which may be populated in any of the ptes
>> + * of the contig range. We are guarranteed to be holding the PTL, so any
>> + * contiguous range cannot be unfolded or otherwise modified under our
>> + * feet.
>> + */
>> +
>> + pte_t pte;
>> + int i;
>> +
>> + ptep = contpte_align_down(ptep);
>> +
>> + for (i = 0; i < CONT_PTES; i++, ptep++) {
>> + pte = __ptep_get(ptep);
>> +
>> + /*
>> + * Deal with the partial contpte_ptep_get_and_clear_full() case,
>> + * where some of the ptes in the range may be cleared but others
>> + * are still to do. See contpte_ptep_get_and_clear_full().
>> + */
>> + if (pte_val(pte) == 0)
>> + continue;
>> +
>> + if (pte_dirty(pte))
>> + orig_pte = pte_mkdirty(orig_pte);
>> +
>> + if (pte_young(pte))
>> + orig_pte = pte_mkyoung(orig_pte);
>> + }
>> +
>> + return orig_pte;
>> +}
>
> Here we need something like this, in order to get it to build in all
> possible configurations:
>
> EXPORT_SYMBOL_GPL(contpte_ptep_get);
>
> (and a corresponding "#include linux/export.h" at the top of the file).
>
> Because, the static inline functions invoke this routine, above.
A quick grep through the drivers directory shows:
ptep_get() is used by:
- drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
- drivers/misc/sgi-gru/grufault.c
- drivers/vfio/vfio_iommu_type1.c
- drivers/xen/privcmd.c
ptep_set_at() is used by:
- drivers/gpu/drm/i915/i915_mm.c
- drivers/xen/xlate_mmu.c
None of the other symbols are called, but I guess it is possible that out of
tree modules are calling others.
So on the basis that these symbols were previously pure inline, I propose to
export all the contpte_* symbols using EXPORT_SYMBOL() so that anything that was
previously calling them successfully continue to do so. Will include in v2.
Thanks,
Ryan
>
> thanks,
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