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 3D8143D3339 for ; Mon, 31 Aug 2026 09:46:18 +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=1788169579; cv=none; b=rVsG2XLs5YtyPQy44xCW48jUCDShsd/yTyjSrDjaMlui1r0XL4wz8RGo1YX3S4s1F8e4ETob7FBP+fYdJjyW60+UgRpD5t8OG1+1inbpvRzXCswqkpNF8dFzMZQUmVaJtfzYRQO6C2zNAgoExcR4H6sGrXthXOGOuu+6ctIlI00= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788169579; c=relaxed/simple; bh=w5JQMu4brjfO4oEbVbybCJUYv7lvKRqcZLwoHT1n4gc=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=fk48nizp3uhhGkgeNhU9xWh2dWfF5LhyfrPQOuVSm3ApjOd67BUWzvNnwHyC0v4z5QEXeRILgCKKIiYTFg+pk9Ijt5N3pryHWsaxL9yoHYJDbcXKZr/PqFGQNHAyH1fgc6HyalDMzKrQeeWZt0NrNMYNaO5NX0VDLv54HjfHPks= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DFozu4Ur; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="DFozu4Ur" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 080281F000E9; Mon, 31 Aug 2026 09:46:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788169578; bh=vuRH3okFqpVfHNcse9s0fjgkHIwVRawZ8XAdlXHNyXU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=DFozu4UrAiFyexHRH2zquy4w4RXQ+MiRV42rq8WA0cCgcSs4xx2BUx796mVaL7jz7 Zf/tsRRTywiEOadLY2ecGWn869ajFax8DqvAA3y34juABmM8Uq9b5m74QlqfBLdJLj V0HzkN0xFipMX8qtvogh9ZVIy+t29ZCmRoCdkN+aVk3Y2AtfIwTsJNSZF9t0O8HLBg 2U3EtySpBXiFXc+Ym93wQZwCUNxI0284MSw2OJwEIgHwNOtoW19aV3tj2+WBQShWZq 8k9fmkhCnTn/VKcq379wojMCyK6n5A/ykUp+dRVFl5xgMY1SeMLC8Cm+67UWBWTR3U Orhv7fKBUaiMA== Message-ID: Date: Mon, 31 Aug 2026 11:46:14 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/slab: reject unsupported kmalloc() sizes Content-Language: en-US To: Zi Yan , Harry Yoo , Andrew Morton , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Alan Stern , Greg Kroah-Hartman Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260830-limit_kmalloc_size-v2-1-bf4ca9c63c88@nvidia.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 8/31/26 04:23, Zi Yan wrote: > kmalloc() is used to allocate physically contiguous memory for kernel > allocations. For requests larger than KMALLOC_MAX_CACHE_SIZE, kmalloc() > uses the page allocator and can only support up to KMALLOC_MAX_SIZE. For > request sizes bigger than KMALLOC_MAX_SIZE, the page allocator can emit a > WARN because kmalloc() allocates an order greater than MAX_PAGE_ORDER. To > make the KMALLOC_MAX_SIZE limit more explicit instead of relying on the > page allocator check, add a KMALLOC_MAX_SIZE check inside kmalloc() to emit > a WARN and return NULL for requested sizes bigger than KMALLOC_MAX_SIZE. > Like the WARN in the page allocator and kvmalloc(), allow __GFP_NOWARN to > suppress the WARN. > > Suggested-by: "Vlastimil Babka (SUSE)" > Signed-off-by: Zi Yan Thanks, added to mm/slab.git slab/for-next > --- > Instead of passing requests greater than KMALLOC_MAX_SIZE to the page > allocator, reject them early inside kmalloc(). > --- > Changes in v2: > 1. Rejected kmalloc() request sizes bigger than KMALLOC_MAX_SIZE by > emitting a WARN and returning NULL inside kmalloc(). The WARN can be > suppressed by __GFP_NOWARN. So the page allocator will no longer see > excessively large requests from kmalloc(). > - Link to v1: https://patch.msgid.link/20260817-limit_kmalloc_size-v1-1-5bef487701cc@nvidia.com > --- > mm/slub.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) > > diff --git a/mm/slub.c b/mm/slub.c > index f9b56cb439e70..23e57a8fe55b4 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -5342,7 +5342,12 @@ static void *___kmalloc_large_node(size_t size, gfp_t flags, int node) > { > struct page *page; > void *ptr = NULL; > - unsigned int order = get_order(size); > + unsigned int order; > + > + if (WARN_ON_ONCE_GFP(size > KMALLOC_MAX_SIZE, flags)) > + return NULL; > + > + order = get_order(size); > > if (unlikely(flags & GFP_SLAB_BUG_MASK)) > flags = kmalloc_fix_flags(flags); > > --- > base-commit: cee9395acd8043be0644b25c34bfa86623f2b935 > change-id: 20260817-limit_kmalloc_size-3a4a2c73beac > > Best regards, > -- > Yan, Zi >