kasan, page_alloc: allow skipping memory init for HW_TAGS

Add a new GFP flag __GFP_SKIP_ZERO that allows to skip memory
initialization.  The flag is only effective with HW_TAGS KASAN.

This flag will be used by vmalloc code for page_alloc allocations backing
vmalloc() mappings in a following patch.  The reason to skip memory
initialization for these pages in page_alloc is because vmalloc code will
be initializing them instead.

With the current implementation, when __GFP_SKIP_ZERO is provided,
__GFP_ZEROTAGS is ignored.  This doesn't matter, as these two flags are
never provided at the same time.  However, if this is changed in the
future, this particular implementation detail can be changed as well.

Link: https://lkml.kernel.org/r/0d53efeff345de7d708e0baa0d8829167772521e.1643047180.git.andreyknvl@google.com


Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Acked-by: Marco Elver <elver@google.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Evgenii Stepanov <eugenis@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Collingbourne <pcc@google.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>