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b=kKWrxb4UfOYype6XihUVGv5QYEukedHvuEXBMMTmSdtlZK+u8xZTaUY5RUTnI1Nl/ gc2cW0K/elejz0o99g0cUUpJs4fLpD8yzFtMBuqEYcNmb8OX6OQW/11eTkngH7HUAt X7/LhU/ydvmeposd4O3TjVtgVJTjTkrmNPO1Z8oJZZhgt8N4O8NpwKr7IfuF50JuDH 5RTnz1UmZM4JebcnLs5zMboRLHa3Ds2mamNBRaHaXflJ+pz4G/4qWmn2SmrD+kmGpA /UIr8wFhCkY+TVoyyyCVA11M8RUeQdBErLp/igtmOGrQbMo0ktUoCNrbQWeKvTTSFZ xiLJfW1AjA5bQ== From: "David Hildenbrand (Arm)" To: stable@vger.kernel.org Cc: linux-mm@kvack.org, "David Hildenbrand (Arm)" , Jane Chu , Harry Yoo , Oscar Salvador , Jann Horn , Liu Shixin , Muchun Song , Andrew Morton , Rik van Riel , Laurence Oberman , Lance Yang , Miaohe Lin , James Houghton , Lukas Bulwahn , Mike Kravetz , Muchun Song Subject: [PATCH 5.10.y 2/7] mm/hugetlb: make detecting shared pte more reliable Date: Wed, 18 Feb 2026 14:05:47 +0100 Message-ID: <20260218130552.55727-3-david@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260218130552.55727-1-david@kernel.org> References: <2026012610-absolve-ducktail-3c64@gregkh> <20260218130552.55727-1-david@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 7EC222001C X-Stat-Signature: i13txwwnfnxqugyahhwy4kxfxnyu5ns7 X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1771419970-287450 X-HE-Meta: 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 GqbU5H2z elTEIN9NTkNenhBJGREzs0VZW9A9CxcwxRZp7OCAUhKQBGJads42+/l5tsyEy+WagAFWYPuwPKC5biFhdrO8cmW4qql7D889FLk3KttlKh2hgrUv+dYomET3xUL/ACQFYFcQQET3jBz+xEKUX30Lqdp/LOAIIUGRwSQu38PuG4cGBv6LaI2R0dWHSwGG9blyyAxQRdEeiDb2Cp2HSR/4RUfkFQnLOOSM64avQAk7X53zrukUR5gyfvWowds5lBiE3+xk2DHkdHPfu+1EquuHTzUficWfw3rTmekRn94XwXNqfB8AEo91SVOpXGObWRKzu4NJYqB17VKVofCyTWHii4sMG/MTEGXxc7KLkLRhBWlPJveTk9uRrUUMtVj5A/rqpp+1/W5cuBFAWYMdFVwPQs+PlfwDpUdQFHieCsBzkqVRaY/CTrUVDFH1Rboxd4+KEw49JcG8Ep1Yuru8= 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) [ David: We don't have 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm", so there are some contextual conflicts. ] Signed-off-by: David Hildenbrand (Arm) --- mm/hugetlb.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 99a71943c1f6..a2cab8f2190f 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -3827,7 +3827,7 @@ static bool is_hugetlb_entry_hwpoisoned(pte_t pte) 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; int cow; @@ -3867,27 +3867,22 @@ 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); - 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) || -- 2.43.0