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b=WPZyX1P06ncN7ohxau8IAqQhLuNlBAz4PPzAKX50qNhkWdcc4cmC7HcKmOrcb9GV5 Fi0r4sPBd/qvGFxMGYKrnYhRp9UND1K8i6wPYWmDEqwP6rGo1TCpaxsW4I8m8Qa68D 5WT+hcZQwpQzInpI2o3Q4dBVXg8UC7YCZzwKqY0uHsH0tYJBrwHIrDPku/+tFLKKhk 6VSqVTwFYLENOlwgOSBFvBuk0kx92H25JzLBPYbTTZ263Zs+95SbiYgzu1IZbJqHJd B68yT17ThRUd1lQnspzkE77ctLEhmWxxGE+JbP5vWDdVDLRw050NTKr2noUiVoo/ll n9o761p2ow3lQ== Message-ID: Date: Mon, 29 Jun 2026 10:05:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/5] mm/page_vma_mapped: use huge_ptep_get() for hugetlb To: Lance Yang , dev.jain@arm.com Cc: linmiaohe@huawei.com, muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, riel@surriel.com, vbabka@kernel.org, harry@kernel.org, jannh@google.com, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcampbell@nvidia.com, apopple@nvidia.com, ziy@nvidia.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, mel@csn.ul.ie, nao.horiguchi@gmail.com, ak@linux.intel.com, j-nomura@ce.jp.nec.com, pfalcato@suse.de, dave.hansen@intel.com, tglx@kernel.org, jpoimboe@kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org References: <0fabee2a-edb7-41c8-91ec-8cf0646c9e83@kernel.org> <20260629074802.42727-1-lance.yang@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 07F80140005 X-Stat-Signature: g9m8yenp3fitm5xtq8f4jhtybts9otan X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1782720346-292441 X-HE-Meta: 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 DTYdbt9l 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/29/26 09:48, Lance Yang wrote: > > On Mon, Jun 29, 2026 at 09:25:48AM +0200, David Hildenbrand (Arm) wrote: >> On 6/29/26 08:48, Dev Jain wrote: >>> >>> >>> >>> Sashiko notes other places: >>> >>> https://sashiko.dev/#/patchset/20260625112955.3254283-1-dev.jain%40arm.com >> >> Yeah, that looks shaky. We do seem to have a bunch of these cases, primarily >>from pagewalk code (where some users like pagemap need the actual address). > > Indeed ... > >> I think we have two options >> >> 1) To prevent any (further) issues, make huge_ptep_get() always consume the >> hstate, and let the arch code deal with aligning it. Invasive. > > Kinda lean toward option 1, even if it's more invasive. If we pass the > hstate down, each arch can figure out the right addr from there. > >> 2) Make the arch code handle aligning without the hstate. >> >> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c >> index 30772a909aea3..303a1b74796c9 100644 >> --- a/arch/arm64/mm/hugetlbpage.c >> +++ b/arch/arm64/mm/hugetlbpage.c >> @@ -126,6 +126,9 @@ pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) >> return orig_pte; >> >> ncontig = find_num_contig(mm, addr, ptep, &pgsize); >> + ptep = PTR_ALIGN_DOWN(ptep, sizeof(*ptep) * ncontig); >> + orig_pte = __ptep_get(ptep); >> + >> for (i = 0; i < ncontig; i++, ptep++) { >> pte_t pte = __ptep_get(ptep); >> >> (nshift/order instead of ncontig might avoid a multiplication, but not sure if that matters in practice) >> >> IIUC, that's similar to what huge_ptep_get() does on ppc. >> >> >> static inline pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) >> { >> if (ptep_is_8m_pmdp(mm, addr, ptep)) >> ptep = pte_offset_kernel((pmd_t *)ptep, ALIGN_DOWN(addr, SZ_8M)); >> return ptep_get(ptep); >> } >> >> I'd assume we could do the same on riscv. Besides that, I don't think any arch has cont >> entries. > > AFAICT, for huge_ptep_get() the addr users are arm64 and powerpc, riscv > doesn't really care about addr there. Looks mostly arm64-specific ... powerpc handles it correctly in the weird "span two PMD entries" case by aligning the PMD down. Risc-v copied from arm64, but can simply derive the #entries from the PTE value. it doesn't have to re-walk the table using the address. But I think the following is required to fix, no? diff --git a/arch/riscv/mm/hugetlbpage.c b/arch/riscv/mm/hugetlbpage.c index a6d217112cf46..7e25cc13b3dba 100644 --- a/arch/riscv/mm/hugetlbpage.c +++ b/arch/riscv/mm/hugetlbpage.c @@ -5,6 +5,7 @@ #ifdef CONFIG_RISCV_ISA_SVNAPOT pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) { - unsigned long pte_num; + unsigned long pte_num, pte_order; int i; pte_t orig_pte = ptep_get(ptep); @@ -12,7 +13,11 @@ pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) if (!pte_present(orig_pte) || !pte_napot(orig_pte)) return orig_pte; - pte_num = napot_pte_num(napot_cont_order(orig_pte)); + pte_order = napot_cont_order(orig_pte); + pte_num = napot_pte_num(pte_order); + + ptep = PTR_ALIGN_DOWN(ptep, sizeof(*ptep) << pte_order); + orig_pte = ptep_get(ptep); for (i = 0; i < pte_num; i++, ptep++) { pte_t pte = ptep_get(ptep); I'd prefer (2) as a simple stable fix first. If we do (1) on top, huge_ptep_get() on arm64 could stop walking the page table another time. If we pass the hstate (or vma) to set_huge_pte_at(), huge_pte_clear(), huge_ptep_get_and_clear(), we could likely get rid of the re-walk in num_contig_ptes() entirely and possibly just remove it. That would probably be cleanest. -- Cheers, David