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Thu, 26 Feb 2026 06:16:57 -0800 (PST) Received: from localhost ([154.47.23.70]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-82739ba6275sm3012040b3a.0.2026.02.26.06.16.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Feb 2026 06:16:56 -0800 (PST) Date: Thu, 26 Feb 2026 22:16:47 +0800 From: Chris Down To: Andrew Morton Cc: David Hildenbrand , Matthew Wilcox , kernel-team@fb.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: [PATCH v2 2/3] mm/huge_memory: Prevent huge zeropage refcount corruption in PMD move Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/2.2.15 (2b349c5e) (2025-10-02) X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 34DC31C000A X-Stat-Signature: xadi3yfr9gt6fqod6rp44714jgjuxoaw X-Rspam-User: X-HE-Tag: 1772115418-903936 X-HE-Meta: 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 IhXdZYdE 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: After commit d82d09e48219 ("mm/huge_memory: mark PMD mappings of the huge zero folio special"), moved huge zero PMDs must remain special so vm_normal_page_pmd() continues to treat them as special mappings. move_pages_huge_pmd() currently reconstructs the destination PMD in the huge zero page branch, which drops PMD state such as pmd_special() on architectures with CONFIG_ARCH_HAS_PTE_SPECIAL. As a result, vm_normal_page_pmd() can treat the moved huge zero PMD as a normal page and corrupt its refcount. Instead of reconstructing the PMD from the folio, derive the destination entry from src_pmdval after pmdp_huge_clear_flush(), then handle the PMD metadata the same way move_huge_pmd() does for moved entries by marking it soft-dirty and clearing uffd-wp. Fixes: d82d09e48219 ("mm/huge_memory: mark PMD mappings of the huge zero folio special") Cc: stable@vger.kernel.org Signed-off-by: Chris Down --- mm/huge_memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index fed57951a7cd..8166b5e871ad 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -2794,7 +2794,8 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm _dst_pmd = pmd_mkwrite(pmd_mkdirty(_dst_pmd), dst_vma); } else { src_pmdval = pmdp_huge_clear_flush(src_vma, src_addr, src_pmd); - _dst_pmd = folio_mk_pmd(page_folio(src_page), dst_vma->vm_page_prot); + _dst_pmd = move_soft_dirty_pmd(src_pmdval); + _dst_pmd = clear_uffd_wp_pmd(_dst_pmd); } set_pmd_at(mm, dst_addr, dst_pmd, _dst_pmd); -- 2.51.2