From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E626A37CD21; Thu, 3 Sep 2026 04:14:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788408866; cv=none; b=IYCjoDv8eSg/8hoMH35Mg1URifteSXo3Le9NhfXwaRX13jKS8RviWGQco6NtgBHaW2chb5cmzQW56LRyaJWg5oIgjhXX2I2jADSkGaoQfQkZuYokb2sD9c43vzMInu1NDQkm0Bm/jj7K6HVH/B9f5vUV12QAH2izHW3auhh97yQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788408866; c=relaxed/simple; bh=eG7XwCvlXryH5rAfF7mveTO/FpMe58WtNzzxletXP0s=; h=Date:To:From:Subject:Message-Id; b=YwAcPWW+RmarWp88t7K7sg6UuefuZnJ3AGOyGxdOaXfQxm6CJYBDXYDIWVXLQL0a0ISU01sIDpmDM+A/GhS4n0xwaP9D4O+ZdTC7q/8HiiTSo9OkGWodXfKlvbf4A35n1GBqUPnCKWEtoO92S1X4KAeHPIpmxmIGpb86QxcjUHQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=JCzo4FBw; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="JCzo4FBw" Received: by smtp.kernel.org (Postfix) with ESMTPSA id BCF261F000E9; Thu, 3 Sep 2026 04:14:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1788408862; bh=Y+4UE3Q8YJmIHGrNwd2eSiyT9P58jvJ+JNvzmjjQC2E=; h=Date:To:From:Subject; b=JCzo4FBw0QzJhbkeI2AIuopUK1z2sn8GJjwcKH9Ew6fD4WjOXILRELtIKhbJpcbTH f6ZfFNm7Fld/L8PcoBaWZiRlpwRowzufZAp6KOKEpZymPHTEb2GX8w7v8HX2+zXhHB sUA8mg6+ue1l6inNzWcGetYhGwPOjzpapreWJouk= Date: Wed, 02 Sep 2026 21:14:22 -0700 To: mm-commits@vger.kernel.org,yu-cheng.yu@intel.com,vbabka@kernel.org,tglx@linutronix.de,stable@vger.kernel.org,rppt@kernel.org,rick.p.edgecombe@intel.com,orsonpeters@gmail.com,ljs@kernel.org,liam@infradead.org,jannh@google.com,david@kernel.org,dave.hansen@linux.intel.com,yanglincheng@kylinos.cn,akpm@linux-foundation.org From: Andrew Morton Subject: + x86-mm-fix-pmd_modify-dropping-the-dirty-bit.patch added to mm-new branch Message-Id: <20260903041422.BCF261F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: x86/mm: fix pmd_modify() dropping the dirty bit has been added to the -mm mm-new branch. Its filename is x86-mm-fix-pmd_modify-dropping-the-dirty-bit.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/x86-mm-fix-pmd_modify-dropping-the-dirty-bit.patch This patch will later appear in the mm-new branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Note, mm-new is a provisional staging ground for work-in-progress patches, and acceptance into mm-new is a notification for others take notice and to finish up reviews. Please do not hesitate to respond to review feedback and post updated versions to replace or incrementally fixup patches in mm-new. The mm-new branch of mm.git is not included in linux-next If a few days of testing in mm-new is successful, the patch will me moved into mm.git's mm-unstable branch, which is included in linux-next Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: Vernon Yang Subject: x86/mm: fix pmd_modify() dropping the dirty bit Date: Thu, 3 Sep 2026 11:16:08 +0800 pmd_modify() masks the old value with (_HPAGE_CHG_MASK & ~_PAGE_DIRTY), silently discarding the hardware dirty bit. The subsequent pmd_mksaveddirty() call is supposed to transfer _PAGE_DIRTY into _PAGE_SAVED_DIRTY when write-protecting, but the dirty bit was already stripped from the value, so there is nothing left to transfer. Contrast with pte_modify(), which keeps _PAGE_DIRTY_BITS in its mask, and pud_modify(), which keeps _HPAGE_CHG_MASK untouched: pmd_modify() is the odd one out. Any pmd_modify() on a writable, dirty PMD loses the dirty state. One visible consequence is data loss with MADV_FREE on PMD-mapped THP: memset(buf, 0x5A, size); // PMD-mapped THP, PMD dirty madvise(buf, size, MADV_FREE); // PMD cleaned but left writable, // folio marked lazyfree memset(buf, 0x5A, size); // hardware sets _PAGE_DIRTY again mprotect(buf, size, PROT_READ); // pmd_modify() drops the dirty bit mprotect(buf, size, PROT_READ|PROT_WRITE); // ... memory pressure ... Reclaim (e.g. under memcg pressure) then finds the lazyfree folio with no dirty bit set anywhere and frees it in __discard_anon_folio_pmd_locked(), even though the data was rewritten after MADV_FREE; subsequent reads fault in fresh zero pages. NUMA hinting alone can trigger the same loss, as do_huge_pmd_numa_page() restores the PMD through pmd_modify() as well. PMD-mapped file THPs are affected too: mprotect()/NUMA hinting dropping the dirty bit means rewritten data is never written back. Fix it by keeping _PAGE_DIRTY in the preserved mask, exactly like pte_modify() and pud_modify() do. The existing pmd_mksaveddirty()/pmd_clear_saveddirty() pair then performs the hardware-dirty <-> saved-dirty transition based on the write bit, preserving the shadow-stack encoding rules. Link: https://lore.kernel.org/20260903031608.1194238-1-vernon2gm@gmail.com Fixes: bb3aadf7d446 ("x86/mm: Start actually marking _PAGE_SAVED_DIRTY") Reported-by: Orson Peters Closes: https://lore.kernel.org/r/CAJxLxMUGu1-L+O_nAONOwOXnS=cNbNApCWqdthRjd76LThtSPg@mail.gmail.com/ Signed-off-by: Vernon Yang Cc: Thomas Gleixner Cc: Dave Hansen Cc: David Hildenbrand Cc: "Edgecombe, Rick P" Cc: Jann Horn Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Mike Rapoport Cc: Vlastimil Babka Cc: Yu-cheng Yu Cc: Signed-off-by: Andrew Morton --- arch/x86/include/asm/pgtable.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/include/asm/pgtable.h~x86-mm-fix-pmd_modify-dropping-the-dirty-bit +++ a/arch/x86/include/asm/pgtable.h @@ -806,7 +806,7 @@ static inline pmd_t pmd_modify(pmd_t pmd pmdval_t val = pmd_val(pmd), oldval = val; pmd_t pmd_result; - val &= (_HPAGE_CHG_MASK & ~_PAGE_DIRTY); + val &= _HPAGE_CHG_MASK; val |= check_pgprot(newprot) & ~_HPAGE_CHG_MASK; val = flip_protnone_guard(oldval, val, PHYSICAL_PMD_PAGE_MASK); _ Patches currently in -mm which might be from yanglincheng@kylinos.cn are mm-khugepaged-fix-swap-entry-value-to-folio_pfn.patch mm-khugepaged-fix-folio-is-used-after-pte_unmap_unlock.patch mm-khugepaged-fix-folio-is-used-after-folio_put-unlock.patch x86-mm-fix-pmd_modify-dropping-the-dirty-bit.patch