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 --- mm/vmalloc.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/vmalloc.c b/mm/vmalloc.c index c607307c657a6..1baa602a0b9bb 100644 --- a/mm/vmalloc.c +++ b/mm/vmalloc.c @@ -4041,7 +4041,10 @@ 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 = kasan_hw_tags_enabled() && + (gfp_mask & __GFP_SKIP_KASAN); + + if (kasan_hw_tags_enabled() && !skip_kasan) { /* * Modify protection bits to allow tagging. * This must be done before mapping. @@ -4057,7 +4060,8 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align, } /* Take note that the mapping is PAGE_KERNEL. */ - kasan_flags |= KASAN_VMALLOC_PROT_NORMAL; + if (!skip_kasan) + kasan_flags |= KASAN_VMALLOC_PROT_NORMAL; } /* Allocate physical pages and map them into vmalloc space. */ -- 2.47.3