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>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index bc6d5a9..2f69ae4 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -168,9 +168,9 @@
.macro mte_set_kernel_gcr, tmp, tmp2
#ifdef CONFIG_KASAN_HW_TAGS
-alternative_if_not ARM64_MTE
+alternative_cb kasan_hw_tags_enable
b 1f
-alternative_else_nop_endif
+alternative_cb_end
mov \tmp, KERNEL_GCR_EL1
msr_s SYS_GCR_EL1, \tmp
1:
@@ -178,10 +178,10 @@
.endm
.macro mte_set_user_gcr, tsk, tmp, tmp2
-#ifdef CONFIG_ARM64_MTE
-alternative_if_not ARM64_MTE
+#ifdef CONFIG_KASAN_HW_TAGS
+alternative_cb kasan_hw_tags_enable
b 1f
-alternative_else_nop_endif
+alternative_cb_end
ldr \tmp, [\tsk, #THREAD_MTE_CTRL]
mte_set_gcr \tmp, \tmp2
