vmalloc: add __GFP_SKIP_KASAN support

Patch series "kasan: hw_tags: Disable tagging for stack and page-tables",
v4.

Stacks and page tables are always accessed with the match-all tag, so
assigning a new random tag every time at allocation and setting invalid
tag at deallocation time, just adds overhead without improving the
detection.

With __GFP_SKIP_KASAN the page keeps its poison tag and KASAN_TAG_KERNEL
(match-all tag) is stored in the page flags while keeping the poison tag
in the hardware.  The benefit of it is that 256 tag setting instruction
per 4 kB page aren't needed at allocation and deallocation time.

Thus match-all pointers still work, while non-match tags (other than
poison tag) still fault.

__GFP_SKIP_KASAN only skips for KASAN_HW_TAGS mode, so coverage is
unchanged.

Benchmark:
The benchmark has two modes. In thread mode, the child process forks
and creates N threads. In pgtable mode, the parent maps and faults a
specified memory size and then forks repeatedly with children exiting
immediately.

Thread benchmark:
2000 iterations, 2000 threads:	2.575 s → 2.229 s (~13.4% faster)

The pgtable samples:
- 2048 MB, 2000 iters		19.08 s → 17.62 s (~7.6% faster)


This patch (of 3):

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 is ignored for them in
the page allocator, and in vmalloc too we ignore this flag for them.

This is a preparatory patch for optimizing kernel stack allocations.

Link: https://lore.kernel.org/[email protected]
Link: https://lore.kernel.org/[email protected]
Signed-off-by: Muhammad Usama Anjum <[email protected]>
Co-developed-by: Ryan Roberts <[email protected]>
Signed-off-by: Ryan Roberts <[email protected]>
Co-developed-by: Dev Jain <[email protected]>
Signed-off-by: Dev Jain <[email protected]>
Reviewed-by: Catalin Marinas <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Ben Segall <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Dietmar Eggemann <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Juri Lelli <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: K Prateek Nayak <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: "Uladzislau Rezki (Sony)" <[email protected]>
Cc: Valentin Schneider <[email protected]>
Cc: Vincent Guittot <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

include/linux/gfp_types.h

@@ -281,9 +281,9 @@ enum {
  *
  * %__GFP_SKIP_KASAN makes KASAN skip unpoisoning on page allocation.
  * Used for userspace and vmalloc pages; the latter are unpoisoned by
- * kasan_unpoison_vmalloc instead. For userspace pages, results in
- * poisoning being skipped as well, see should_skip_kasan_poison for
- * details. Only effective in HW_TAGS mode.
+ * kasan_unpoison_vmalloc instead. If passed to vmalloc, kasan_unpoison_vmalloc
+ * is skipped too. For userspace pages, results in poisoning being skipped as
+ * well, see should_skip_kasan_poison for details. Only effective in HW_TAGS mode.
  */
 #define __GFP_NOWARN	((__force gfp_t)___GFP_NOWARN)
 #define __GFP_COMP	((__force gfp_t)___GFP_COMP)

mm/vmalloc.c

@@ -3933,7 +3933,7 @@ fail:
 				__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)
 {
@@ -3974,6 +3974,9 @@ 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
  */
@@ -3987,6 +3990,7 @@ 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 = kasan_hw_tags_enabled() && (gfp_mask & __GFP_SKIP_KASAN);
 
 	if (WARN_ON_ONCE(!size))
 		return NULL;
@@ -4017,7 +4021,7 @@ void *__vmalloc_node_range_noprof(unsigned long size, unsigned long align,
 again:
 	area = __get_vm_area_node(size, align, shift, VM_ALLOC |
 				  VM_UNINITIALIZED | vm_flags, start, end, node,
-				  gfp_mask, caller);
+				  gfp_mask & ~__GFP_SKIP_KASAN, caller);
 	if (!area) {
 		bool nofail = gfp_mask & __GFP_NOFAIL;
 		warn_alloc(gfp_mask, NULL,
@@ -4035,7 +4039,7 @@ again:
 	 * 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.
@@ -4072,7 +4076,8 @@ again:
 	    (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