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h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RiX+CxxKVDl7Rb4MNf49jz/6t05hRkytgOqO+xc2+t+f11crdaEumCECCXRTd43AY InZMBcZiQG5/XIcJ0kZTkNqYfxbik2UHF3kkTr13zeAtpwslDXRvplwYLq0o1Dg2My K2YzBzVjMSVn65AogUa5fm3mwX0rf4mgaQhjGojE= Message-ID: <91e38f4d-652a-486f-aeff-6b955b43c193@arm.com> Date: Mon, 27 Apr 2026 09:04:36 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/3] vmalloc: add __GFP_SKIP_KASAN support To: Catalin Marinas 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 References: <20260424130157.3163009-1-dev.jain@arm.com> <20260424130157.3163009-2-dev.jain@arm.com> Content-Language: en-US From: Dev Jain In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 573C3A0002 X-Stat-Signature: fpajsx6y3it5p8iu6xetite3p3xtjxjj X-HE-Tag: 1777260915-643650 X-HE-Meta: U2FsdGVkX199+KeLBm3N7E9y9u8xP5MeM02vikBDwpdJ8vdFv+kvErvUy3Y53wE+wPKLcGP8qrOdjqQuRSMihB/4Czof8gu8Tzf6rx0qAUYjpb/kkt55zrQjfx0nu2/RrqpbbP6agi1JJcq2YJAYS95WNbJPBORkfaSY/EyubTNFExwbPEKg1IPJZcH2UuakIRcH7q7+vIgGMKhq4Yyiw2G8Sv4fiBWKFvnxZ5zI1Tk3oinLOs9idtfGwELQed5Us3usUpqHHSQY6+NAccC587+nxX4+0mAjfyVDxvd656XDtFbBSDqyT0qkSGQfa9CaKR0ejvIdcKCftzUPsHz7FoC2TQxgC8OFf67g5Pz/yUiG0xhJbrAsYYD0nKuKGmvfkTF07qyjUPvJS5NobkIFoVQjY3S9YqB+z8fH6qU1xslZVxE50NUPdJKNOo5/VXv0dcguKA/t4qpO7PAkReke7PVpoEyJ9URXeohvo5HBPUs8DaLVhiKwKpWGQD2NDHZJiRfkywBB3wQit5ZLaL+2Oo0woDj0uk3BNB0mlz8gx1kmLFnstDf0D7pKAKa2/SMxs/FAn5rK/8Zj3XUUmouwP66F1AE2TrblebaeGgZOE1zrXiHI/lGIutS+I1kTgxLD0Jy8PT/2s93D272d0xwmN8vkDoYn7ilSa1bTPozQ3TrNj1E6tRhLXxomWVrnm3oJlYgxNakkCHsUhSuRRIwV7TLlI6Q2haHwCFV4bJ5+BzLvucuTEtY9OIzN2nVIXd4MnsV84tji0SJ1jSUOgkF4wsf/XMglVFVbhO6AKsXCHOPrPQINwU1mai+nBIGuN3SdVXlsQy48mnBS2GF2uIx9abHzWVwkqfs6PKwh4KsBrFTTZzjMVETXVx/lHX7cGdTjQWYwzGuPvWP/qb6UBHn4Pw98fHjMJwv2M1N9fprsw/wy02DQy5YZpSXaDMejN+5hTwnCGVQHzS3NKVMg2Vp bD2mlE/q ugP/InaYvxXchtBL6TYa06L3KRIMRqapIRG+auXcp5GQv+lTS2lyyNMRCTzVYo+CcKIGfeql5sDZmWTjQ82PaWjD4zLy65dMuZpG/QfUFdcNFfkSprUsyrnWBaZxqhXOAe24pKvcBP4kyvzzNtLNSEaftkIoj0qPwHboEYo85QvvqcuN2KtbszZ/OUi1EI420a6tmU9Cdt3dqvQ12ta2haPdMnjpWDD34C0vDL5+fowUatj9C+2YYYbqnomKQCpOhyqgfWHpQqyGk53Ozu0V/nPaW5F8tICrfx9Wm4nv2bHGeElM5iQhbxr0h12t677luNjZMFCtRdpuMp2rCYXVp+E/4JSyHp9lG/JXsPdt+v4Rg2+mBcYfbaVtL59vtkk9Pg/6y Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 25/04/26 12:02 am, Catalin Marinas wrote: > 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. oops I forgot, I'll do that. > >> --- >> 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. Okay I'll do this. > > 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. Lemme reply on the other reply >