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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 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; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260830-limit_kmalloc_size-v2-1-bf4ca9c63c88@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5D1C114000B X-Stat-Signature: eozak3arqi1gdstjz8c1eap6b9fjcpst X-HE-Tag: 1788169579-486929 X-HE-Meta: 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 +WN9rlbZ zJ8pb8Jtr/SkWyHrevu5Uy9iza20XI91KuUHddvbbtB9BGky0Kh4PKdPScSWefjuTaGi8l4U15X4LLgGIxDsQwr5kMHQzd7tG1HIptZYWlRsADOBZm7fXVHvoIFuWNxP0K1R9G3O+hOugcBsmlw8LgrofTk15rOEvJ4sZovGdiGHlkOyDu4qtC4te0Gr27y1ZXp39bEIs4+Rbjr8kUYnVrJfoy1x9QQHg2cBhqTDdnvXWt7mLZ918/tA+nv+27jw1qRtPddWcmWVCSO+iibMjM/annqYybUhpXcb1e/kxa4nUhP9R8IR4Za+LdzBlHM78QRDjDT/7p7btIaEWwvriP4puN9X4fg6LO/Mul22HNFGU6nT4D8zJjOGtnBc/ttQCwqNQOmVi16YrZOY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 >