[PATCH v3 1/3] vmalloc: add __GFP_SKIP_KASAN support

[Dev Jain <dev.jain@arm.com>]

From: Muhammad Usama Anjum <usama.anjum@arm.com>

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 <ryan.roberts@arm.com>
Co-developed-by: Dev Jain <dev.jain@arm.com>
Signed-off-by: Muhammad Usama Anjum <usama.anjum@arm.com>
---
 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;
 		}
 
 		/* Take note that the mapping is PAGE_KERNEL. */
@@ -4078,7 +4091,8 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align,
 	    (gfp_mask & __GFP_SKIP_ZERO))
 		kasan_flags |= KASAN_VMALLOC_INIT;
 	/* KASAN_VMALLOC_PROT_NORMAL already set if required. */
-	area->addr = kasan_unpoison_vmalloc(area->addr, size, kasan_flags);
+	if (!skip_vmalloc_kasan)
+		area->addr = kasan_unpoison_vmalloc(area->addr, size, kasan_flags);
 
 	/*
 	 * In this function, newly allocated vm_struct has VM_UNINITIALIZED
-- 
2.34.1