From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 95E093644DE for ; Thu, 20 Nov 2025 16:52:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763657550; cv=none; b=SUS4do2Rq5bTt1ruSx3UOyHnk6P7eC8Y3YkVKxO2ynW7PFIPYeMrI5kPX24ZlKFN/p9NQhUUzMUOdsFaCZV0tJnD/pwmZ4YxBqBLPziKmm23MVW4j1yJGhfzMCLSCu+F5q6vrEMaFPd0Fx780ftHeskUl1xT7FFyOAmTD/bUI4k= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763657550; c=relaxed/simple; bh=N+K3lg+dXve7J1ZBkHqK/XJmq06JJMJQcDco4KZUEe8=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=NOyJAzlGnjJZaO7Nd009zq7Wo+RQzG2aQNIbOhnLVYvAGdlAt/60z47Qky83ZMzN5u8GKGFlnFC5+qP2HVAc3h4bDVlHuCCaYeVS2S+2H0AStp+g3j/r7wdaTFAGV+dAZzBNNQx4CqoL6HyFtkW8ejIhjpXtPAc6oOtpmkG8Fes= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=QU24d2/Q; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="QU24d2/Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 12501C116C6; Thu, 20 Nov 2025 16:52:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763657550; bh=N+K3lg+dXve7J1ZBkHqK/XJmq06JJMJQcDco4KZUEe8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QU24d2/QoVJ2/U+fQFbkqISCLTxcUFMr7U4QxaTBOhvWBa+FzVWg4oJ+FCq1yKMkO NiBayXqVuK7NX7QUlAv8lFfSbGQONcWNlkUm64WHFf5rknJtcLU2WAEdFKBJnOiLfQ zb7R9TnHF4+yyfJly4biwdmAIsFm8z/JLjhYYGOaUMzqLpYaUu+5WCbtjpGQGPd/lk /g6yYr0+X8zAaQsvwUzRAGmMVRpeMAZg5jxE9vKtFhwtg0qq09C/le75E+p4MGg+YF n4hz3kgBtSpQONzys244+9fxzJOReNo09nOSftcx0HrpsN+STFYI/tzFKbnKU5bHt0 2YvxFhJUI7H0Q== Received: from phl-compute-02.internal (phl-compute-02.internal [10.202.2.42]) by mailfauth.phl.internal (Postfix) with ESMTP id 54607F4006A; Thu, 20 Nov 2025 11:52:29 -0500 (EST) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-02.internal (MEProxy); Thu, 20 Nov 2025 11:52:29 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtdeggddvvdejieduucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhephffvvefufffkofgjfhgggfestdekredtredttdenucfhrhhomhepmfhirhihlhcu ufhhuhhtshgvmhgruhcuoehkrghssehkvghrnhgvlhdrohhrgheqnecuggftrfgrthhtvg hrnhepgeejffehvdeltdefteejieehveeuffeuteevhfehvdejieelteffleefleeiffeh necuffhomhgrihhnpehkvghrnhgvlhdrohhrghenucevlhhushhtvghrufhiiigvpedtne curfgrrhgrmhepmhgrihhlfhhrohhmpehkihhrihhllhdomhgvshhmthhprghuthhhphgv rhhsohhnrghlihhthidqudeiudduiedvieehhedqvdekgeeggeejvdekqdhkrghspeepkh gvrhhnvghlrdhorhhgsehshhhuthgvmhhovhdrnhgrmhgvpdhnsggprhgtphhtthhopedv tddpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtohepshhtrggslhgvsehvghgvrhdrkh gvrhhnvghlrdhorhhgpdhrtghpthhtohepkhgrsheskhgvrhhnvghlrdhorhhgpdhrtghp thhtohepvhhirhhoseiivghnihhvrdhlihhnuhigrdhorhhgrdhukhdprhgtphhtthhope gsrgholhhinhdrfigrnhhgsehlihhnuhigrdgrlhhisggrsggrrdgtohhmpdhrtghpthht ohepsghrrghunhgvrheskhgvrhhnvghlrdhorhhgpdhrtghpthhtohepughjfihonhhgse hkvghrnhgvlhdrohhrghdprhgtphhtthhopegurghvihgusehfrhhomhhorhgsihhtrdgt ohhmpdhrtghpthhtohepuggrvhhiugesrhgvughhrghtrdgtohhmpdhrtghpthhtohephh hughhhugesghhoohhglhgvrdgtohhm X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 20 Nov 2025 11:52:28 -0500 (EST) From: Kiryl Shutsemau To: stable@vger.kernel.org Cc: Kiryl Shutsemau , Al Viro , Baolin Wang , Christian Brauner , "Darrick J. Wong" , Dave Chinner , David Hildenbrand , Hugh Dickins , Johannes Weiner , Liam Howlett , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , Rik van Riel , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton Subject: [PATCH 6.17.y] mm/truncate: unmap large folio on split failure Date: Thu, 20 Nov 2025 16:52:21 +0000 Message-ID: <20251120165221.892852-1-kas@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025112037-resurface-backlight-da75@gregkh> References: <2025112037-resurface-backlight-da75@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Accesses within VMA, but beyond i_size rounded up to PAGE_SIZE are supposed to generate SIGBUS. This behavior might not be respected on truncation. During truncation, the kernel splits a large folio in order to reclaim memory. As a side effect, it unmaps the folio and destroys PMD mappings of the folio. The folio will be refaulted as PTEs and SIGBUS semantics are preserved. However, if the split fails, PMD mappings are preserved and the user will not receive SIGBUS on any accesses within the PMD. Unmap the folio on split failure. It will lead to refault as PTEs and preserve SIGBUS semantics. Make an exception for shmem/tmpfs that for long time intentionally mapped with PMDs across i_size. Link: https://lkml.kernel.org/r/20251027115636.82382-3-kirill@shutemov.name Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios") Signed-off-by: Kiryl Shutsemau Cc: Al Viro Cc: Baolin Wang Cc: Christian Brauner Cc: "Darrick J. Wong" Cc: Dave Chinner Cc: David Hildenbrand Cc: Hugh Dickins Cc: Johannes Weiner Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport Cc: Rik van Riel Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton (cherry picked from commit fa04f5b60fda62c98a53a60de3a1e763f11feb41) Signed-off-by: Kiryl Shutsemau --- mm/truncate.c | 34 ++++++++++++++++++++++++++++------ 1 file changed, 28 insertions(+), 6 deletions(-) diff --git a/mm/truncate.c b/mm/truncate.c index 91eb92a5ce4f..95fb291526fc 100644 --- a/mm/truncate.c +++ b/mm/truncate.c @@ -177,6 +177,31 @@ int truncate_inode_folio(struct address_space *mapping, struct folio *folio) return 0; } +static int try_folio_split_or_unmap(struct folio *folio, struct page *split_at) +{ + enum ttu_flags ttu_flags = + TTU_SYNC | + TTU_SPLIT_HUGE_PMD | + TTU_IGNORE_MLOCK; + int ret; + + ret = try_folio_split(folio, split_at, NULL); + + /* + * If the split fails, unmap the folio, so it will be refaulted + * with PTEs to respect SIGBUS semantics. + * + * Make an exception for shmem/tmpfs that for long time + * intentionally mapped with PMDs across i_size. + */ + if (ret && !shmem_mapping(folio->mapping)) { + try_to_unmap(folio, ttu_flags); + WARN_ON(folio_mapped(folio)); + } + + return ret; +} + /* * Handle partial folios. The folio may be entirely within the * range if a split has raced with us. If not, we zero the part of the @@ -224,7 +249,7 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) return true; split_at = folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE); - if (!try_folio_split(folio, split_at, NULL)) { + if (!try_folio_split_or_unmap(folio, split_at)) { /* * try to split at offset + length to make sure folios within * the range can be dropped, especially to avoid memory waste @@ -248,13 +273,10 @@ bool truncate_inode_partial_folio(struct folio *folio, loff_t start, loff_t end) if (!folio_trylock(folio2)) goto out; - /* - * make sure folio2 is large and does not change its mapping. - * Its split result does not matter here. - */ + /* make sure folio2 is large and does not change its mapping */ if (folio_test_large(folio2) && folio2->mapping == folio->mapping) - try_folio_split(folio2, split_at2, NULL); + try_folio_split_or_unmap(folio2, split_at2); folio_unlock(folio2); out: -- 2.51.0