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b=WAioAEop8PvlX0aN+H42ku2aA/91uZ2+X+OFiD+gYB5KrXphyNuGFEql8U2CwZOOB xuDvlffJvNe2ESHvIOx+y3/rQYcUgowkbQAKb5MZR0zrsQ0xLx+RJ0uYtc7YM33sU3 Nmg8/DJkF4EeJrXBxBnnF1eStxDnlRMdeFAYzOhKdjFAZN6jVGcy6pWnGBpj2GDZPf w5mvZH55aMxuuVUqqjTycLCq6VPgMy3KFl06H8ebVxprQCYtZgBTILT+We6sXy0O6J /wot86el/wnhkbKFYJl2P90TKpXscqWgpJ8tZzlGKaNjTX73ODe094Q+C1ww80GmPO u077j2bqbpK5Q== From: "David Hildenbrand (Arm)" To: stable@vger.kernel.org Cc: linux-mm@kvack.org, Miaohe Lin , Lukas Bulwahn , Mike Kravetz , Muchun Song , Andrew Morton , David Hildenbrand Subject: [PATCH 5.15.y 1/6] mm/hugetlb: make detecting shared pte more reliable Date: Wed, 18 Feb 2026 12:01:24 +0100 Message-ID: <20260218110129.41578-2-david@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260218110129.41578-1-david@kernel.org> References: <2026012608-tulip-moisten-c6f6@gregkh> <20260218110129.41578-1-david@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Stat-Signature: a6h51qq8euqxautaod3gysieb8exk385 X-Rspam-User: X-Rspamd-Queue-Id: 6A19540012 X-Rspamd-Server: rspam01 X-HE-Tag: 1771412500-734431 X-HE-Meta: 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 K5pfW7F7 vzHBGEgm/tMyaUt2SIVwYOlkySZ2us0tL3REiM7oA/XO25/mFugXNEyqp2yVwi9xcmaGVjkz03J+om8YLob29HQRo9UxLMZC0Z6InueKnaZdagh8CjPs2nBKx2pTH1Tne6Qwr27FCx7hpreSDcF3M6hOYqi3G92YDey0/ooEC7wWoS6jxAEwr21C5W3FgKf/6+GC3kEHj7ZB9uSvOftm1yvbsEES7PL7Kp/IwVGAhXsvCLddo3boYNMbN2RXeQ+hMqV6gATQlDFnW2qyKI7r9kZ5MadW2DS8viBytka/SrtB0V9qpesbPqA7k1vnhQO2xKrq+g/yrwCiZrFJEeVtTQPDA0GDMFzmIry3GcBm0ejEmtb59UPHX1yGZAQJ67Qu6U2KvhLa5yevfRJWZVyXhuTZg47sKOFePWiVM4E57j6VgoVUbQFnkD570zrpXVrNeSaWmIe8Z2fBZl24= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: From: Miaohe Lin If the pagetables are shared, we shouldn't copy or take references. Since src could have unshared and dst shares with another vma, huge_pte_none() is thus used to determine whether dst_pte is shared. But this check isn't reliable. A shared pte could have pte none in pagetable in fact. The page count of ptep page should be checked here in order to reliably determine whether pte is shared. [lukas.bulwahn@gmail.com: remove unused local variable dst_entry in copy_hugetlb_page_range()] Link: https://lkml.kernel.org/r/20220822082525.26071-1-lukas.bulwahn@gmail.com Link: https://lkml.kernel.org/r/20220816130553.31406-7-linmiaohe@huawei.com Signed-off-by: Miaohe Lin Signed-off-by: Lukas Bulwahn Reviewed-by: Mike Kravetz Cc: Muchun Song Signed-off-by: Andrew Morton (cherry picked from commit 3aa4ed8040e1535d95c03cef8b52cf11bf0d8546) Signed-off-by: David Hildenbrand (Arm) --- mm/hugetlb.c | 21 ++++++++------------- 1 file changed, 8 insertions(+), 13 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 70ceac102a8d..c0719ece2b7f 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4304,7 +4304,7 @@ hugetlb_install_page(struct vm_area_struct *vma, pte_t *ptep, unsigned long addr int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, struct vm_area_struct *vma) { - pte_t *src_pte, *dst_pte, entry, dst_entry; + pte_t *src_pte, *dst_pte, entry; struct page *ptepage; unsigned long addr; bool cow = is_cow_mapping(vma->vm_flags); @@ -4343,28 +4343,23 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, /* * If the pagetables are shared don't copy or take references. - * dst_pte == src_pte is the common case of src/dest sharing. * + * dst_pte == src_pte is the common case of src/dest sharing. * However, src could have 'unshared' and dst shares with - * another vma. If dst_pte !none, this implies sharing. - * Check here before taking page table lock, and once again - * after taking the lock below. + * another vma. So page_count of ptep page is checked instead + * to reliably determine whether pte is shared. */ - dst_entry = huge_ptep_get(dst_pte); - if ((dst_pte == src_pte) || !huge_pte_none(dst_entry)) + if (page_count(virt_to_page(dst_pte)) > 1) continue; dst_ptl = huge_pte_lock(h, dst, dst_pte); src_ptl = huge_pte_lockptr(h, src, src_pte); spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); entry = huge_ptep_get(src_pte); - dst_entry = huge_ptep_get(dst_pte); again: - if (huge_pte_none(entry) || !huge_pte_none(dst_entry)) { + if (huge_pte_none(entry)) { /* - * Skip if src entry none. Also, skip in the - * unlikely case dst entry !none as this implies - * sharing with another vma. + * Skip if src entry none. */ ; } else if (unlikely(is_hugetlb_entry_migration(entry) || @@ -4423,7 +4418,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, restore_reserve_on_error(h, vma, addr, new); put_page(new); - /* dst_entry won't change as in child */ + /* huge_ptep of dst_pte won't change as in child */ goto again; } hugetlb_install_page(vma, dst_pte, addr, new); -- 2.43.0