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Sat, 12 Sep 2026 07:38:05 +0000 X-Mizu-Trace-ID: 937d4987c72d0ac1 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: yintirui@gmail.com Cc: akpm@linux-foundation.org, linux-mm@kvack.org, david@kernel.org, ljs@kernel.org, dev.jain@arm.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, lance.yang@linux.dev, ryan.roberts@arm.com, nico.pache@linux.dev, usama.arif@linux.dev, liam@infradead.org, wangkefeng.wang@huawei.com, chenjun102@huawei.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC 4/9] mm/huge_memory: use normal_or_softleaf_folio_pmd() in the PMD split path Date: Sat, 12 Sep 2026 15:37:55 +0800 Message-Id: <20260912073755.8403-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.39.3 (Apple Git-146) In-Reply-To: References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: 1EFC0180009 X-Stat-Signature: ypkj516db8zcb113m9mqjtc9yuwr1xx1 X-Rspamd-Server: rspam01 X-HE-Tag: 1789198696-693723 X-HE-Meta: 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 IH7Ozo0m LpvTsXy5i8MfhOLfGByat8mWNCINI1nJWuonovOuH9PwFr2QSvf7Xib6xnNbBs+lShTrlO2bFJwJqPahVQ/IXGSqKqfUPxoauO8Jqc18qnecHeWAsMTb/IrUoec0+B2lsAHu2Zx+u0oVTL/++P6ZVR8dJAG/l9tbA3pzj/yVc1ScBk95FMi4KH+c3BI+jFUZImDBAPRO0Mmm9mem80Fz4YL/5bBmaP0D/pHTFosgqmJF0bndUCXZM9g9QXbn55u8AizyOUde3EHalTwscctDGNF3gE1eiuV2dYDXaNv4EN2UMIVYu4mcUwSKU1g== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, Aug 29, 2026 at 02:33:14AM +0800, Yin Tirui wrote: >Get the folio once with normal_or_softleaf_folio_pmd() and decide the >deposit once with has_deposited_pgtable(), as zap_huge_pmd() does. That >makes split and zap classify an entry the same way, and drops >vma_is_special_huge() from this path. > >Behaviour changes only where the entry and the VMA flags disagree, which no >in-tree path produces. > >Signed-off-by: Yin Tirui >--- > mm/huge_memory.c | 21 ++++++++++++--------- > 1 file changed, 12 insertions(+), 9 deletions(-) > >diff --git a/mm/huge_memory.c b/mm/huge_memory.c >index aefd62827139..b2ede9a6ae5d 100644 >--- a/mm/huge_memory.c >+++ b/mm/huge_memory.c >@@ -3172,7 +3172,7 @@ static void unmap_huge_pmd_entry(struct vm_area_struct *vma, > * We are going to unmap this huge page. So > * just go ahead and zap it > */ >- if (arch_needs_pgtable_deposit()) >+ if (has_deposited_pgtable(vma, old_pmd, folio)) > zap_deposited_table(mm, pmd); Staring at this ... I think we're missing raw PFN mappings of the huge zero folio ... static bool has_deposited_pgtable(struct vm_area_struct *vma, pmd_t pmdval, struct folio *folio) { /* Some architectures require unconditional depositing. */ if (arch_needs_pgtable_deposit()) return true; ... if (is_huge_zero_pmd(pmdval)) return !vma_is_dax(vma); ... return folio && folio_test_anon(folio); } If a non-DAX raw PFN mapping on x86 (say, via mshv_vtl_low) matches huge_zero_pfn, vmf_insert_pfn_pmd() won't deposit a page table, but has_deposited_pgtable() will return true ... Before this patch, arch_needs_pgtable_deposit() skips withdrawal when splitting this mapping on x86. The new check would instead reach pgtable_trans_huge_withdraw() and dereference NULL through pgtable->lru if pmd_huge_pte(mm, pmd) is NULL. The helper already causes the same bug in zap_huge_pmd(), but extending it to split is a regression introduced by this patch. I'll send a separate fix, and we need it landed first :D [...] Cheers, Lance