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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Fiyz70s4+uUmNIjX6xDSUdsEK140AT1ai79NuNO+FWxq+cbpgHt9EB8jc7BkLtcU9 0K71n9prgUrk/y4KNQgNrLb42LI0u/iktK1roYgs9wWn3PE9SaEULIHo9SXT8C4g/+ gn+oSZCYkUxpoyK2BiuJDr9vOdIKKu/7eKYah7ME= Message-ID: Date: Tue, 30 Jun 2026 19:23:54 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/5] mm/page_vma_mapped: use huge_ptep_get() for hugetlb To: "David Hildenbrand (Arm)" , Lance Yang 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> <6fdc0cbd-0880-4594-bf33-a2993ac2fe60@arm.com> <1fb04774-1ac6-472a-bbc8-52fceb69b018@kernel.org> Content-Language: en-US From: Dev Jain In-Reply-To: <1fb04774-1ac6-472a-bbc8-52fceb69b018@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: C0BC4180010 X-Rspam-User: X-Stat-Signature: g9ak56qi9awf1csgzp9jia6e1ken9ju7 X-HE-Tag: 1782827646-286815 X-HE-Meta: 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 2mKVJTEN 6nNAXghLYXUGbgcoVWRS9taJ2n1yFmtZWeDnz4UXGT07H1oLh4/k/rdK5dVZQ6I+x3SXimZTuSPQYHgbxfVgIHYpCQB257SL+q1UISpX6+3+u1odxJyDU1IRZdIF9sud9PxN3+o41Cb61fUrtYJz4WmcynP5A0pXR8FO6RYJvRjitKJ4/hmlVIaPAz+AM4w/rAFJ7M6PhSLXXVP4+uCLUDEn+u0vLPazaI4vbQP+VsD3RfqqPRMEMr11jTP70lURXwpyzURmlGQPzEtrjVdSF5oz1BD3NzRcL37PL3BLyNmIK2OvwJqUN/HlqLpVco8RSmWLbX5K8VMjM40hf4GQpBbGzEAn4HrkdDC2JI+MjVISs2k0= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 30/06/26 6:16 pm, David Hildenbrand (Arm) wrote: > On 6/30/26 13:34, Dev Jain wrote: >> >> >> On 29/06/26 1:35 pm, David Hildenbrand (Arm) wrote: >>> On 6/29/26 09:48, Lance Yang wrote: >>>> >>>> >from pagewalk code (where some users like pagemap need the actual address). >>>> >>>> Indeed ... >>>> >>>> >>>> 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. >>>> >>>> >>>> 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? >> >> We don't receive an unaligned ptep in huge_ptep_get, and riscv derives the >> number of cont ptes from the pte itself, so why is the below required? > > Let me look at the actual report once more ... > > I thought for a second that the problem would be having the ptep not point at the > start of the hugetlb page mapping. But that should always be the case. > So yes, riscv does not have any problems. > > And IIUC, arm64 only has a problem when CONT_PTES != CONT_PMDS (16 kernel?). > > Yeah, aligning the ptep down doesn't solve anything, it's already properly aligned. > > To fix it inside arm64 code, we'd have to teach find_num_contig() to > ignore the ptep and instead look for the cont bit, maybe? > > But I'm sure I messed this up as I am working on 10 things at the same time :D > > > diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c > index d477a9dd1b472..d1d03795c135e 100644 > --- a/arch/arm64/mm/hugetlbpage.c > +++ b/arch/arm64/mm/hugetlbpage.c > @@ -76,7 +76,7 @@ bool arch_hugetlb_migration_supported(struct hstate *h) > #endif > > static int find_num_contig(struct mm_struct *mm, unsigned long addr, > - pte_t *ptep, size_t *pgsize) > + size_t *pgsize) > { > pgd_t *pgdp = pgd_offset(mm, addr); > p4d_t *p4dp; > @@ -87,7 +87,7 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr, > p4dp = p4d_offset(pgdp, addr); > pudp = pud_offset(p4dp, addr); > pmdp = pmd_offset(pudp, addr); > - if ((pte_t *)pmdp == ptep) { > + if (pmd_cont(*pmdp)) { We can simply do this right: diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c index b8432886085af..a35fa373263dc 100644 --- a/arch/arm64/mm/hugetlbpage.c +++ b/arch/arm64/mm/hugetlbpage.c @@ -87,7 +87,7 @@ static int find_num_contig(struct mm_struct *mm, unsigned long addr, p4dp = p4d_offset(pgdp, addr); pudp = pud_offset(p4dp, addr); pmdp = pmd_offset(pudp, addr); - if ((pte_t *)pmdp == ptep) { + if ((pte_t *)PTR_ALIGN_DOWN(pmdp, sizeof(*pmdp) * CONT_PMDS) == ptep) { *pgsize = PMD_SIZE; return CONT_PMDS; } > *pgsize = PMD_SIZE; > return CONT_PMDS; > } > @@ -131,7 +131,7 @@ pte_t huge_ptep_get(struct mm_struct *mm, unsigned long addr, pte_t *ptep) > if (!pte_present(orig_pte) || !pte_cont(orig_pte)) > return orig_pte; > > - ncontig = find_num_contig(mm, addr, ptep, &pgsize); > + ncontig = find_num_contig(mm, addr, &pgsize); > for (i = 0; i < ncontig; i++, ptep++) { > pte_t pte = __ptep_get(ptep); > > @@ -475,7 +475,7 @@ void huge_ptep_set_wrprotect(struct mm_struct *mm, > return; > } > > - ncontig = find_num_contig(mm, addr, ptep, &pgsize); > + ncontig = find_num_contig(mm, addr, &pgsize); > > pte = get_clear_contig_flush(mm, addr, ptep, pgsize, ncontig); > pte = pte_wrprotect(pte); > diff --git a/mm/memory.c b/mm/memory.c > >