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imf15.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=HxgT6fUn; spf=pass (imf15.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1776110580; a=rsa-sha256; cv=none; b=aNDkPHgpAeBr64PDLVPMp5jP46FBmyEVu+i+ZQ8/c8mTEO/dEt9N3MgFEneDhCOzt17d7v qazrT3XPtemiy1D6sVRW9DtZ9JV0kajMhLlZLTdFBP9j7mRmOi5tujeo1t5cnyQPgRQtgp ZTckxP54PM+w0wIC29NCQP5cAihvOG0= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 0018F61843; Mon, 13 Apr 2026 20:03:00 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 98D03C2BCAF; Mon, 13 Apr 2026 20:02:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776110579; bh=X5Qr7RMZPcVsHaB67sBlEm7JbLFMJ0dv+rLoHvobS5U=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=HxgT6fUn+5kb5WwLOPN7Ze+RMzag6T9eul66Jd1aQhH3Ac+bnWH7NDyXrPyemABdp I/Iqc9Wmid5rK7bX78l6MdpPYYovFk6XcU+m9MXNu2B9lQ3AE/CKKoV407TZ7lYy5y ikjD7iopCPr000/vOdpw0eZ54kJ9LYsQxZIKjB5FzBynfxPRKf3vWruvwKWB3kUiOg B3L96qx/q21+cISIF5UZsBJ6QF2HiTjat5Owme2y6anfyX/m7HxUJAVm5jFQNS131i rE0oVtcBGYt4MEJCQDvGJUk6vIPguYRBddrEDPSx+80OIt4jrDXHePx/EBqg2x6Zoj 2ayc1/HcJ6uSA== Message-ID: <9886b2c6-5516-4be8-ac31-db3133455af2@kernel.org> Date: Mon, 13 Apr 2026 22:02:41 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v3 4/4] mm: add PMD-level huge page support for remap_pfn_range() To: Yin Tirui , linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, willy@infradead.org, catalin.marinas@arm.com, will@kernel.org, tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, luto@kernel.org, peterz@infradead.org, akpm@linux-foundation.org, lorenzo.stoakes@oracle.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, Liam.Howlett@oracle.com, npache@redhat.com, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, anshuman.khandual@arm.com, rmclure@linux.ibm.com, kevin.brodsky@arm.com, apopple@nvidia.com, ajd@linux.ibm.com, pasha.tatashin@soleen.com, bhe@redhat.com, thuth@redhat.com, coxu@redhat.com, dan.j.williams@intel.com, yu-cheng.yu@intel.com, yangyicong@hisilicon.com, baolu.lu@linux.intel.com, jgross@suse.com, conor.dooley@microchip.com, Jonathan.Cameron@huawei.com, riel@surriel.com Cc: wangkefeng.wang@huawei.com, chenjun102@huawei.com References: <20260228070906.1418911-1-yintirui@huawei.com> <20260228070906.1418911-5-yintirui@huawei.com> 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-Rspam-User: X-Stat-Signature: a999fbk1wfkh8g11c5hcw8s5uhjk8c7t X-Rspamd-Queue-Id: C1AA6A001F X-Rspamd-Server: rspam09 X-HE-Tag: 1776110580-621228 X-HE-Meta: U2FsdGVkX1+HxUjQN1sr/2o2e0TDylRiHiatHuGEEdLhXLiAS+q7xESv+H4HCeVs3c/fmPY8s7WFc8jOAbE8iMgKed9CbK3cU8Mj+1eo23qcXJl0Xi0A7XMpP3/RvDw5syJTSReg/BFRVSw10tFfk1OjnrmNjl61qCsnq38kdCW0Nh3qGUs5FbNtJ/lVKHIEsFJEE89ZsOcPMwtrknfVZxTyftOhH5XG/vAAglpFinFnGbHVWBR4MxuLcRiTJeZTs1uCgBqIGLt6Y9FnsHfC9VnrjmFr3E/XsyGfeadW3P1FrCQWKMWg6u7yfnPGTXykBN+OBymiK4MjV/EjFA4kZuRwTpq5OSCXoH9M5OnOC3tHNl2S4Zx2QBLBGUgrtpGJHi1pvVkPOt30vjCNkTwnE0zFVUMva4gcZ9mC+nvBNNPij14weD5zXDf65ArrB9GR43dtQ4oWy6W7JFZVcssfz22w80T6FjHsRilxawJVlJUr4dFGq/a88SIMxbce5dV+STJUcX+eJA9ylYRAq2E0K4NCkuNb6tjfrNmJwen/3ZCYjf3q1+ote7VcnvWHKReJ5URoP2HQQ8zp17bxCAT0gJjKnRN8U43oAyUuacHDon9hYl0keBNq/FpGhUl9N1XTnlntkYeUs7wN11uNLuSvBSVwmAcxLJnbl7SXuKaX+l1KkL1XRZ4nZ0K/inPqTiZAQvMudGve0rIq+wlMupJw708xGQcbhFLnuDASbmI6Q9hbzdhN/UBLa7OEKflFHMObqj1MG83CWhxlt7oL49xzjTKQM99SYpS91Bne025GOr/Nz3Pdv1AcVejEWdEtiyvS1cmtLsEsFPm5V/pjbG65TgGIplDUfFWLgdJ+NE6fdLROoo5o98k+1PpnkPjKxyQGgm5s5na1q2LcwLPExYkwkdjTBnMvYsMM7uIP9ElSivcbvA5VJrMMfT9l/R0r9qdOf9hZWXXQrZOrFJb/b5w ykN6yoh0 QXjK+f+GMtihMElPPj/kVr6bZZA0TN0TMDbNnmVP9xtr0YSsarqqheoiRnadF/sFPOcIv1rX3C629oFOENxK+WwU6i3ALNOoxOaA5pHmyeUVIMZB3AGzoQroSwsJYYHzXitgVWqs+cLoXSIiwSpthLmciDO14NbVhnKluSMCFWUbBY1IbVdXXW7pt86nm2siTxDghVGpq1awpvTvgeuQ0nEEMRb1OcvQA+1qinBA1PscszN2HmZrqGu4nZ4f+Z/NWAGDywJzpKNy1F4455Qrfb6ggCSuO9uksXisGCx8cg/ovB4rNadxyYDA77iJxJsgUP5bFn7r8kkfHkKrnbYw7mZeZTg28m+GSeb6Sf0L+b/LCzbjGeW1tKr4jB4zZk9mFyTjYxdEq7AUFKi1B073ay9TjYla59PH4qKNg Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/28/26 08:09, Yin Tirui wrote: > Add PMD-level huge page support to remap_pfn_range(), automatically > creating huge mappings when prerequisites are satisfied (size, alignment, > architecture support, etc.) and falling back to normal page mappings > otherwise. > > Implement special huge PMD splitting by utilizing the pgtable deposit/ > withdraw mechanism. When splitting is needed, the deposited pgtable is > withdrawn and populated with individual PTEs created from the original > huge mapping. > > Signed-off-by: Yin Tirui > --- [...] > > if (!vma_is_anonymous(vma)) { > old_pmd = pmdp_huge_clear_flush(vma, haddr, pmd); > + > + if (!vma_is_dax(vma) && vma_is_special_huge(vma)) { These magical vma checks are really bad. This all needs a cleanup (Lorenzo is doing some, hoping it will look better on top of that). > + pte_t entry; > + > + if (!pmd_special(old_pmd)) { If you are using pmd_special(), you are doing something wrong. Hint: vm_normal_page_pmd() is usually what you want. > + zap_deposited_table(mm, pmd); > + return; > + } > + pgtable = pgtable_trans_huge_withdraw(mm, pmd); > + if (unlikely(!pgtable)) > + return; > + pmd_populate(mm, &_pmd, pgtable); > + pte = pte_offset_map(&_pmd, haddr); > + entry = pfn_pte(pmd_pfn(old_pmd), pmd_pgprot(old_pmd)); > + set_ptes(mm, haddr, pte, entry, HPAGE_PMD_NR); > + pte_unmap(pte); > + > + smp_wmb(); /* make pte visible before pmd */ > + pmd_populate(mm, pmd, pgtable); > + return; > + } > + > /* > * We are going to unmap this huge page. So > * just go ahead and zap it > */ > if (arch_needs_pgtable_deposit()) > zap_deposited_table(mm, pmd); > - if (!vma_is_dax(vma) && vma_is_special_huge(vma)) > - return; > + > if (unlikely(pmd_is_migration_entry(old_pmd))) { > const softleaf_t old_entry = softleaf_from_pmd(old_pmd); > > diff --git a/mm/memory.c b/mm/memory.c > index 07778814b4a8..affccf38cbcf 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -2890,6 +2890,40 @@ static int remap_pte_range(struct mm_struct *mm, pmd_t *pmd, > return err; > } > > +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP Why exactly do we need arch support for that in form of a Kconfig. Usually, we guard pmd support by CONFIG_TRANSPARENT_HUGEPAGE. And then, we must check at runtime if PMD leaves are actually supported. Luiz is working on a cleanup series: https://lore.kernel.org/r/cover.1775679721.git.luizcap@redhat.com pgtable_has_pmd_leaves() is what you would want to check. > +static int remap_try_huge_pmd(struct mm_struct *mm, pmd_t *pmd, > + unsigned long addr, unsigned long end, > + unsigned long pfn, pgprot_t prot) Use two-tab indent. (currently 3? :) ) Also, we tend to call these things now "pmd leaves". Call it "remap_try_pmd_leaf" or something even more expressive like "remap_try_install_pmd_leaf()" > +{ > + pgtable_t pgtable; > + spinlock_t *ptl; > + > + if ((end - addr) != PMD_SIZE) if (end - addr != PMD_SIZE) Should work > + return 0; > + > + if (!IS_ALIGNED(addr, PMD_SIZE)) > + return 0; > + You could likely combine both things into a if (!IS_ALIGNED(addr | end, PMD_SIZE)) > + if (!IS_ALIGNED(pfn, HPAGE_PMD_NR)) Another sign that you piggy-back on THP support ;) > + return 0; > + > + if (pmd_present(*pmd) && !pmd_free_pte_page(pmd, addr)) > + return 0; Ripping out a page table?! That doesn't sound right :) Why is that required? We shouldn't be doing that here. Gah. Especially, without any pmd locks etc. > + > + pgtable = pte_alloc_one(mm); > + if (unlikely(!pgtable)) > + return 0; > + > + mm_inc_nr_ptes(mm); > + ptl = pmd_lock(mm, pmd); > + set_pmd_at(mm, addr, pmd, pmd_mkspecial(pmd_mkhuge(pfn_pmd(pfn, prot)))); > + pgtable_trans_huge_deposit(mm, pmd, pgtable); > + spin_unlock(ptl); > + > + return 1; > +} > +#endif > + > static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud, > unsigned long addr, unsigned long end, > unsigned long pfn, pgprot_t prot) > @@ -2905,6 +2939,12 @@ static inline int remap_pmd_range(struct mm_struct *mm, pud_t *pud, > VM_BUG_ON(pmd_trans_huge(*pmd)); > do { > next = pmd_addr_end(addr, end); > +#ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP > + if (remap_try_huge_pmd(mm, pmd, addr, next, > + pfn + (addr >> PAGE_SHIFT), prot)) { Please provide a stub instead so we don't end up with ifdef in this code. -- Cheers, David