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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Catalin Marinas , Will Deacon , Ryan.Roberts@arm.com References: <20260324132631.482520-1-usama.anjum@arm.com> <20260324132631.482520-2-usama.anjum@arm.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david.hildenbrand@arm.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzS1EYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWQuaGlsZGVuYnJhbmRAYXJtLmNvbT7CwY0EEwEIADcWIQQb2cqtc1xM OkYN/MpN3hD3AP+DWgUCaYJpgwIbAwUJJlgIpAILCQQVCgkIAhYCAh4FAheAAAoJEE3eEPcA /4NaGMsP/iLFeIScMoXBTDNlEyrfQQ83cTPahTGF4H+RXK/EdTOezXgCUzADIAyQYuOVZu9A bRBGw4F/mLeCfbFUhdMQnZ7XtHNmKHT3eOfylFiznkzUHAvFs4CaRptXVL2eEn1l6DmV7Sd0 N4yKy4BJoJ01arJOAGKLMTSXPt94SIo1r70bDuiiDHMAcOQ/4pka9D1X6w9aptTYsOWGu0AK 2enfm/KYpBEJlepvKkg4UsdeRlDwRUXxFma8Gd4PhoTD8wcXkeaMk3Qupkg7ge8oaU0gvaOk 8WxY+sIDGXf2xvVqZk8klzX8uGydW0GOxw3h0TIz12GCgi3uXaN4Y3C2CQJlM+ThqBrhJGNE KPsme2RzknpcuKsJAj5DByZyT0FZdrLF3NsrgwEM72A/gIKSDkzhW9OOfg7mnIhF53LfrKVd /RYUYVq4p2mGkcSGo/aolitmLxflbXcPNypT+S66i4+sgyExUsv+QRNacXtuacdPyQNk3pnM n37ZANdADP9KLVtfIBvI6iYyTH+B2C8U9JcrMGgaqkBONOEz03mfbBnBCLA8oBZqudBLOF3s amcIE5dVBj3OP8o2vuU8FKgiP/6cWSNUY/+Mg95XLGUAl8xTN+n4sohkPrGzR+1t8oVLsab0 Y+absub5T4UIl09wk29ClBMYz82uyDzwDAqxf4XuzkSUzsFNBFXLn5EBEADn1959INH2cwYJ v0tsxf5MUCghCj/CA/lc/LMthqQ773gauB9mN+F1rE9cyyXb6jyOGn+GUjMbnq1o121Vm0+n eKHUCBtHyseBfDXHA6m4B3mUTWo13nid0e4AM71r0DS8+KYh6zvweLX/LL5kQS9GQeT+QNro XcC1NzWbitts6TZ+IrPOwT1hfB4WNC+X2n4AzDqp3+ILiVST2DT4VBc11Gz6jijpC/KI5Al8 ZDhRwG47LUiuQmt3yqrmN63V9wzaPhC+xbwIsNZlLUvuRnmBPkTJwwrFRZvwu5GPHNndBjVp AfaSTOfppyKBTccu2AXJXWAE1Xjh6GOC8mlFjZwLxWFqdPHR1n2aPVgoiTLk34LR/bXO+e0G pzFXT7enwyvFFFyAS0Nk1q/7EChPcbRbhJqEBpRNZemxmg55zC3GLvgLKd5A09MOM2BrMea+ l0FUR+PuTenh2YmnmLRTro6eZ/qYwWkCu8FFIw4pT0OUDMyLgi+GI1aMpVogTZJ70FgV0pUA lpmrzk/bLbRkF3TwgucpyPtcpmQtTkWSgDS50QG9DR/1As3LLLcNkwJBZzBG6PWbvcOyrwMQ UF1nl4SSPV0LLH63+BrrHasfJzxKXzqgrW28CTAE2x8qi7e/6M/+XXhrsMYG+uaViM7n2je3 qKe7ofum3s4vq7oFCPsOgwARAQABwsF8BBgBCAAmAhsMFiEEG9nKrXNcTDpGDfzKTd4Q9wD/ g1oFAmic2qsFCSZYCKEACgkQTd4Q9wD/g1oq0xAAsAnw/OmsERdtdwRfAMpC74/++2wh9RvV Q0x8xXvoGJwZrk0Jmck1ABIM//5sWDo7eDHk1uEcc95pbP9XGU6ZgeiQeh06+0vRYILwDk8Q /y06TrTb1n4n7FRwyskKU1UWnNW86lvWUJuGPABXjrkfL41RJttSJHF3M1C0u2BnM5VnDuPF QKzhRRktBMK4GkWBvXlsHFhn8Ev0xvPE/G99RAg9ufNAxyq2lSzbUIwrY918KHlziBKwNyLo Pn9kgHD3hRBaYakz87WKUZd17ZnPMZiXriCWZxwPx7zs6cSAqcfcVucmdPiIlyG1K/HIk2LX 63T6oO2Libzz7/0i4+oIpvpK2X6zZ2cu0k2uNcEYm2xAb+xGmqwnPnHX/ac8lJEyzH3lh+pt 2slI4VcPNnz+vzYeBAS1S+VJc1pcJr3l7PRSQ4bv5sObZvezRdqEFB4tUIfSbDdEBCCvvEMB goisDB8ceYxOcFAM8nBWrEmNU2vvIGJzjJ/NVYYIY0TgOc5bS9wh6jKHL2+chrfDW5neLJjY 2x3snF8q7U9GEIbBfNHDlOV8SyhEjtX0DyKxQKioTYPOHcW9gdV5fhSz5tEv+ipqt4kIgWqB gzK8ePtDTqRMqZq457g1/SXSoSQi4jN+gsneqvlTJdzaEu1bJP0iv6ViVf15+qHuY5iojCz8 fa0= In-Reply-To: <20260324132631.482520-2-usama.anjum@arm.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: vHX6JM/wehLx5/bBCRSuog/ZXKaqAa4Sz/BZEgG4RMegzYCSPz2Xmp2YUlm4Fr3hXDXcvN6kX8UtaiM6axXq/QAGmF+tBmFW8zubfhQOQzpbXaGede8XnG6HKnjMYietOjB8G1cUJW4zd0T11pT80BoTZxPeXsVroOwjKkQ8CknLeU5UdlxUIFAkcoqwDGz8G5QtQMB3mial4MnjR5wwEAdIZ/FCh9+t+Qo9ZXjHK9KA97f2wdD9slPmm1iGIK088uJydKmWyLA9Q/3i/bktCunVHzPEEDgLSaH4Dtchh4DcCHifF/w6G8xvh8BsxzgnXmD6bsBVLX0e4HgI6Ya2LE9vdHprn7ggHiJJIU1t2tz8ZkPubX21AwMf4kcItXG7PhvHhoUf1TIZ7vDtwu/lhgBf+cvSs6vrErGgPRqf9m/sXT2fmbnzFLDWePz2qlpi X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 16 Apr 2026 09:12:08.6854 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: d8008bec-5438-4056-1e89-08de9b983ca3 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS0EPF000001AB.eurprd05.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: AM0PR08MB5313 On 3/24/26 14:26, Muhammad Usama Anjum wrote: > 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, don’t skip zeroing the pages and > don’t set KASAN_VMALLOC_PROT_NORMAL so kasan_unpoison_vmalloc() > returns early without tagging. > > 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. > > Signed-off-by: Muhammad Usama Anjum > --- > Changes since v1: > - Simplify skip conditions based on the fact that __GFP_SKIP_KASAN > is zero in non-hw-tags mode. > - Add __GFP_SKIP_KASAN to GFP_VMALLOC_SUPPORTED list of flags > --- > mm/vmalloc.c | 11 ++++++++--- > 1 file changed, 8 insertions(+), 3 deletions(-) > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > index c607307c657a6..69ae205effb46 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 +3980,8 @@ 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 poisoning > + * > * Can not be called from interrupt nor NMI contexts. > * Return: the address of the area or %NULL on failure > */ > @@ -4041,7 +4043,9 @@ 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()) { > + bool skip_kasan = gfp_mask & __GFP_SKIP_KASAN; > + > + if (kasan_hw_tags_enabled() && !skip_kasan) { This code gets ever more ugly. :) After I spotted the horrible ___GFP_SKIP_ZERO that shouldn't even exist, I thought about teaching vmalloc.c to use a sub-allocator interface to the buddy instead, where we would essentially say "leave zeroing and KASAN to the sub-allocator": vmalloc. Then, we'd get rid of ___GFP_SKIP_ZERO and just use __GFP_SKIP_KASAN to decide ourselves here what to do with KASAN. I tried to implement that, but that SW KASAN / !KASAN handling messes with my brain. :) In particular, the order for HW KASAN is currently: a) Allocate pages *and map them*. b) Zero the pages That means that we have temporarily unzeroed pages mapped there. I don't know if that's problematic, but it's one of the differences to SW KASAN / ! KASAN handling here. -- Cheers, David