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bh=QKB3JZ7g2c9VEy/es5AGCSmsO1y75sbX2AXFlGxaubw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HkmEng6MQ0mN5UA/B4zvsQ7CuMkuqsLgFOq/mDQ61S+yV+9yLVau+m1EwCf8rBaKn yJGqU/ulj3zjqHHthJDAF3df4Dg0IsiIC5cW7GeUiLq9O+bCPmUqYVENOByDeOMzxB 4Y4FOiydJWdwx4jFtRbrGsriNSaedpyBC82UGk4Y= Date: Fri, 24 Apr 2026 19:32:13 +0100 From: Catalin Marinas To: Dev Jain Cc: arnd@arndb.de, kees@kernel.org, mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, akpm@linux-foundation.org, david@kernel.org, urezki@gmail.com, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, tglx@kernel.org, usama.anjum@arm.com, mathieu.desnoyers@efficios.com, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Ryan Roberts Subject: Re: [PATCH v3 1/3] vmalloc: add __GFP_SKIP_KASAN support Message-ID: References: <20260424130157.3163009-1-dev.jain@arm.com> <20260424130157.3163009-2-dev.jain@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260424130157.3163009-2-dev.jain@arm.com> X-Rspam-User: X-Rspamd-Queue-Id: 8EC5F40005 X-Rspamd-Server: rspam04 X-Stat-Signature: t7yqo53ozqy7yopqbddrp6ox7bexwc7w X-HE-Tag: 1777055540-467059 X-HE-Meta: U2FsdGVkX1/EZPBUcLKq79F6CVxyMPZ4UWx9RZ4VUbmaA1w+dGQe3OHlH7JzTRP1kuLMtBQ+H7s/J4DQazdr6r2+6enbov2ANkCIs0eSt3AxExG0DIssaKGuBdxYlmnGrPR8epwPZmbctBL+zI3Tx87jGpVRb3/LOsOFUZbtHFNc2JpL67prC0cbdeO2ssHlzYseiIXCGuGAPGGEpanrJK1bSxDoZrY7jxR/0XRJ7WLYDjkEbv2LkxsGqliqDya2Q2zh1JsfDeedbVz40ByGpnXhNF0ygRuzh4GKWesOktsiwsmnAaUdV6XOG47w2DvEhpVYdcTm1SfkoeRRide8z4YEaO6vgF7ij9RewsQd0HMsJ5dLJ84opMZfNGXF3IKkCIU5eIGTbvR34O/6lXI95dio4aq1h8I7cGF7OLthLVWNBO/gjxPMvL0dmqh5au6mOJb6z1V8qrjpTtpj7UR/BWC3Q1oe0GchJ14Md5j0C+bocGxcb4uzdiA97VoS0R1k22yoGGkHgvLyz0Z6PsqCVKgQYo5gZ7PYYe1BKzaiYYmRpZhkqC6jTADu7Edk+8U17KExM+iNi1/dDGCeyQPU0q/hxrGm/xaeGIzNQrVtkOrVy8x07xiXAJ754psKWsdQSZjOhu6EZQoPPQzgtfmVYUTNRuXux1d8fMGnUzlqKVoJDP9/CQt0gpCLLXJ6g2j0+fhQPAIRmm3TSCqehNMHUK4XuaqMxYLMwTyx86XQxUqTMak1PVlRaSCPi97Mq2baJxxYL5dGfpRVhZb08lUW0vaaM2gsCPu4QWQCKvvly/sk6Bbam00CoBHiP1PmLTVIaCowrwrGU9SE4WGR42Sb36ygLWAf7Yi+QYriW3wKbEg+dAWQyl6m6FXfgPRZxU/Hg1shTuoZsjhtZNcKmOAOqVCAVebrrTLzOjSymA+ZPZRJyWJMTCydEb1VpUKZ3NUOUKh0/8/iuJn2grfYm8H qY0SPtbJ UI27TmP6MAArExJbS7qsIRaoiMKlox/8P9jNNZ3SfeE1sOaD6cxjOc8QXuTgfOKzOPRNVloEbdEdBNn4AVPT9QjB0U0j42lzbyw18fL7WeIz9qG7AEe3u3DRey1J+9adkTiFY7DdhvXN85x2xxevakZ4+W2GA0zuxt/MVLNaVn8Ozzk4luoaKKhEZOd+GPOOz4bvN6bJF/sa/XBttSW2ziFzyWJU8fUmbGTq0WBV3aFXdUMpJVGEjEKkygmNdiTL3OO9j6bkNqk5WObOMFl9oOmGT1yQVUFUS3VGg+05BDkDNBiEYoheCt+lBtoWflnnIDqUKhevX6GpvnsvL2kscvERyUAGKWAgcFVTwjHvH+9U3IlPIS8urJM6uXA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Apr 24, 2026 at 06:31:55PM +0530, Dev Jain wrote: > From: Muhammad Usama Anjum > > For allocations that will be accessed only with match-all pointers > (e.g., kernel stacks), setting tags is wasted work. If the caller > already set __GFP_SKIP_KASAN, skip tag setting of vmalloc pages. > > Before this patch, __GFP_SKIP_KASAN wasn't being used with vmalloc > APIs. So it wasn't being checked. Now its being checked and acted > upon. Other KASAN modes are unchanged because __GFP_SKIP_KASAN isn't > defined there. > > This is a preparatory patch for optimizing kernel stack allocations. > > Co-developed-by: Ryan Roberts > Co-developed-by: Dev Jain > Signed-off-by: Muhammad Usama Anjum Co-developers need to sign off as well. See submitting-patches.rst. Same comment about your SoB as on patch 3. > --- > mm/vmalloc.c | 20 +++++++++++++++++--- > 1 file changed, 17 insertions(+), 3 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index b31b208f6ecb3..c94fcb2725b6b 100644 > --- a/mm/vmalloc.c > +++ b/mm/vmalloc.c > @@ -3939,7 +3939,7 @@ static void *__vmalloc_area_node(struct vm_struct *area, gfp_t gfp_mask, > __GFP_NOFAIL | __GFP_ZERO |\ > __GFP_NORETRY | __GFP_RETRY_MAYFAIL |\ > GFP_NOFS | GFP_NOIO | GFP_KERNEL_ACCOUNT |\ > - GFP_USER | __GFP_NOLOCKDEP) > + GFP_USER | __GFP_NOLOCKDEP | __GFP_SKIP_KASAN) > > static gfp_t vmalloc_fix_flags(gfp_t flags) > { > @@ -3980,6 +3980,9 @@ static gfp_t vmalloc_fix_flags(gfp_t flags) > * > * %__GFP_NOWARN can be used to suppress failure messages. > * > + * %__GFP_SKIP_KASAN can be used to skip unpoisoning of mapped pages > + * (when prot=%PAGE_KERNEL). > + * > * Can not be called from interrupt nor NMI contexts. > * Return: the address of the area or %NULL on failure > */ > @@ -3993,6 +3996,10 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align, > kasan_vmalloc_flags_t kasan_flags = KASAN_VMALLOC_NONE; > unsigned long original_align = align; > unsigned int shift = PAGE_SHIFT; > + bool skip_vmalloc_kasan = gfp_mask & __GFP_SKIP_KASAN; > + > + /* Don't skip metadata kasan unpoisoning */ > + gfp_mask &= ~__GFP_SKIP_KASAN; > > if (WARN_ON_ONCE(!size)) > return NULL; > @@ -4041,7 +4048,7 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align, > * kasan_unpoison_vmalloc(). > */ > if (pgprot_val(prot) == pgprot_val(PAGE_KERNEL)) { > - if (kasan_hw_tags_enabled()) { > + if (kasan_hw_tags_enabled() && !skip_vmalloc_kasan) { > /* > * Modify protection bits to allow tagging. > * This must be done before mapping. > @@ -4054,6 +4061,12 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align, > * poisoned and zeroed by kasan_unpoison_vmalloc(). > */ > gfp_mask |= __GFP_SKIP_KASAN | __GFP_SKIP_ZERO; > + } else if (skip_vmalloc_kasan) { > + /* > + * Skip page_alloc unpoisoning physical pages backing > + * VM_ALLOC mapping, as requested by caller. > + */ > + gfp_mask |= __GFP_SKIP_KASAN; > } This playing around with some of the GFP flags meant for metadata and the actual page allocation gets confusing. You remove __GFP_SKIP_KASAN early from gfp_mask, add it back here. You might as well just remove it when calling __get_vm_area_node() and we won't have to figure out why it's added back above. The __GFP_SKIP_ZERO flag is meant for the page allocator and used in this function later to actually tell kasan to initialise the memory (not skip this). __GFP_SKIP_KASAN, OTOH, is used to actually tell both vmalloc() and the underlying page allocator to avoid tagging. I wonder whether it would be better to have a VM_SKIP_KASAN flag instead and leave the GFP flags alone. -- Catalin