FROMGIT: arm64: kasan: mte: move GCR_EL1 switch to task switch when KASAN disabled

It is not necessary to write to GCR_EL1 on every kernel entry and
exit when HW tag-based KASAN is disabled because the kernel will not
execute any IRG instructions in that mode. Since accessing GCR_EL1
can be expensive on some microarchitectures, avoid doing so by moving
the access to task switch when HW tag-based KASAN is disabled.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Acked-by: Andrey Konovalov <andreyknvl@gmail.com>
Link: https://linux-review.googlesource.com/id/I78e90d60612a94c24344526f476ac4ff216e10d2


Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210924010655.2886918-1-pcc@google.com


Signed-off-by: Will Deacon <will@kernel.org>
(cherry picked from commit e5af50a5
 https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/mte)
Change-Id: I0f06de2fce4dea2967c0fee608d1900915493d23
Bug: 192536783