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bh=7mIUdhpxjfBGpDoIwyQsU3lKaGAeN4hJVoywz3Jt11U=; h=From:To:Cc:Subject:Date:From; b=A65Fo0vA4tHeeQXXWFvROS/Qx4WjhFQyKCTP3R+9g1J/pHMVXTLveKpCjWEo0lrP0 LjuuNTfiardA87j/CArqMgKjjdiTuvEsqv9a36VCfwTQm1BjHEBg9Wk4yrRwthoiNE fZ05es2tqrTsRMM8eQqARMz0RPfjPEivtCMlIYJE= From: Dev Jain To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org Cc: Dev Jain , riel@surriel.com, liam@infradead.org, vbabka@kernel.org, harry@kernel.org, jannh@google.com, kas@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, ryan.roberts@arm.com, anshuman.khandual@arm.com, stable@vger.kernel.org Subject: [PATCH] mm/rmap: use huge_ptep_get() in try_to_unmap_one() Date: Thu, 25 Jun 2026 04:28:51 +0000 Message-ID: <20260625042853.2752898-1-dev.jain@arm.com> X-Mailer: git-send-email 2.43.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 0D13520004 X-Stat-Signature: yt9fk7hjtktgmtqxcq4xaex76w86kwn3 X-HE-Tag: 1782361777-990139 X-HE-Meta: U2FsdGVkX19of9wg0uVUd6Q4QzFgd5+Z47AHSpbWsWKlf7j+0OrLDqYBLeQqgLwYvrb7POyytp9SqWdjgbZ8WqHuL8a3wnmm4ZMFChpvQj/zn+QPdETgtYF70rgMBxUqWDTwldu2vE94DwQBAgdAq/nUWBRmS83Lm/nGlOOMas4h3PzBOP7TC+sjtEV5bOEy91yEDvBAp+oH88ZfqEopbGzzJDhvD5MrTtRHWyFClymJWSeLHABM/k3IQUkzI0Ruvk84jbvYR61k4prdcgQ2hCLSRq47LW2OIn4Yxq3oEF5421uH25NL3rqmU1WJESwJ6pZ+Vuv0unmF+z8jOCbjBMAtFoVFZSK1mZH8SwU06rL01E3we/oWZkmbQwWyoWisnW7I1m/Bazv29Q1nDMlbDrm/MZyUzE5TmGJE1Pcqkpcctx3aIy0c6dSH565XRjJkxOUurX0OQFgDyEZ+oE5IAR7V/sJtxY7nZ2ZouIqoxJSLYEu8Kvwbom4pAmi7VBapeZOEQN0hUnPsOhwLnGY53iVcN13vwZIIJtde18SdkCUWE6ffQu8MSQQvDWXfVxlzvqX4ndgeGm67tVNkSGTgHe4g+MrD2IfcpXFmPnQRd9wu6tUSgoEf4SI1ea2xPawN9AcldMRIPI6G/yquQW6CbmRUJj1ZENS4fNF2jpFEJJwPb15UyOWHxphX0rKRgPcgtFJaRGXAQ7RL6JSBteu/lbTyaktLjrkBc2qcfpdNN7EYZsDjAdCzbj17UCS5Y9ojuyi+ChZ5EozytXP/uT100XM1IbKLGvAVGw+M1Ag6t+GHRj7DvuPQxsFSBG/jAmJER7+SYLPwNn6BD5N2P9hAB/jJS8qtNnmK7iaRXYfC6IDRfc+fBuCBIncReN+Vn2ikdam8TKt241GN0+l6UyRVRExYqwo3fAPh5H33xur33uNJx430Ofn+gr0gURrIHEkFb1KcsBpUlLfI+O5NClc nROvf2co yJgy/OCOKbPouaKBJslH9bYV7ax7kFqfQburSj77fSdHSr/uZn/UgUXoYJCRauDED5d/SN0Pmj3yVta4i09XOKtgMzVgpvcqVy/F+U9pM8VMnZNS5JTyqHhPUSV4bVMl+8DeN4Wu9jhWJuVB5SlVxmjAhCE+Gr4H3rWzHNj4jLiJojBJJpjDmQ0hmNA2ivzNn79A2Fxz80/ls166lZWBddPwyxyHLgq+tw6RIn4TPXI/tIrkY3nVN4Zgyz37kKgcIHQQ4FEBailI0a3F1+ymmcAkTNgqwpjj8fkyA0rosIFULqDoJbU/ucWRkm8AtdUJLFuA1 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: try_to_unmap_one() handles hugetlb folios when memory failure needs to replace a poisoned hugetlb mapping with a hwpoison entry. In that case page_vma_mapped_walk() returns the hugetlb entry in pvmw.pte, but the code reads it with ptep_get() before decoding the PFN. That is wrong on architectures where hugetlb entries are not encoded as regular PTEs. On s390, for example, a raw huge RSTE must be converted by huge_ptep_get() before helpers such as pte_pfn() can inspect it. A raw decode can select the wrong subpage, so try_to_unmap_one() can install a hwpoison entry for the wrong PFN. The userspace-visible result is that a later access to the poisoned hugetlb subpage can miss the expected SIGBUS. With DEBUG_VM, the wrong subpage can also trip the PageHWPoison check. Use huge_ptep_get() for hugetlb mappings before decoding the PFN. Before c7ab0d2fdc84, the bug existed in the form of a plain dereference: we would check the head page pfn of the hugetlb with pte_pfn(*pte), and bail out on mismatch. This would mean that the hwpoisoned entry will not get installed. I am not sure what is the procedure on such kinds of very old bugs - how back should I really go? Fixes: c7ab0d2fdc84 ("mm: convert try_to_unmap_one() to use page_vma_mapped_walk()") Cc: stable@vger.kernel.org Signed-off-by: Dev Jain --- Applies on mm-unstable (d17fe8a046a2). There are similar old bugs present, in try_to_migrate_one(), check_pte(), remove_migration_pte(), prot_none_hugetlb_entry(). mm/rmap.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index 1c77d5dc06e9f..aa8a254efaecc 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2095,11 +2095,16 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, /* Unexpected PMD-mapped THP? */ VM_BUG_ON_FOLIO(!pvmw.pte, folio); - /* - * Handle PFN swap PTEs, such as device-exclusive ones, that - * actually map pages. - */ - pteval = ptep_get(pvmw.pte); + address = pvmw.address; + if (folio_test_hugetlb(folio)) { + pteval = huge_ptep_get(mm, address, pvmw.pte); + } else { + /* + * Handle PFN swap PTEs, such as device-exclusive ones, + * that actually map pages. + */ + pteval = ptep_get(pvmw.pte); + } if (likely(pte_present(pteval))) { pfn = pte_pfn(pteval); } else { @@ -2110,7 +2115,6 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma, } subpage = folio_page(folio, pfn - folio_pfn(folio)); - address = pvmw.address; anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(subpage); -- 2.43.0