[PATCH 08/24] arm64: Introduce mte_get_reset_tfsr() helpers

["Pierre-Clément Tosi" <ptosi@google.com>]

In an effort to untangle MTE from KASAN, split a reusable MTE helper out
of mte_check_tfsr_el1(), providing two variants, to accommodate the
contexts under which it gets called: one synchronising TFx before
reading it and another delegating that responsibility to the caller.

Name the helpers similarly to __dsu_pmu_get_reset_overflow().

This prepares for a rework of the KASAN API to simplify circular header
dependencies, as KASAN calls into mte_check_tfsr_el1(), which calls back
into a kasan_*() function.

Signed-off-by: Pierre-Clément Tosi <ptosi@google.com>
---
 arch/arm64/include/asm/mte.h | 31 +++++++++++++++++++++++++++++++
 arch/arm64/kernel/mte.c      | 12 +-----------
 2 files changed, 32 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 1d6113ae786f..614fff7dc35f 100644
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -17,7 +17,9 @@
 #include <linux/sched.h>
 #include <linux/types.h>
 
+#include <asm/barrier.h>
 #include <asm/pgtable-types.h>
+#include <asm/sysreg.h>
 
 void mte_clear_page_tags(void *addr);
 unsigned long mte_copy_tags_from_user(void *to, const void __user *from,
@@ -31,6 +33,35 @@ void mte_invalidate_tags_area(int type);
 void *mte_allocate_tag_storage(void);
 void mte_free_tag_storage(char *storage);
 
+static __always_inline bool __mte_get_reset_tfsr(void)
+{
+	u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
+
+	if (likely(!(tfsr_el1 & SYS_TFSR_EL1_TF1)))
+		return false;
+
+	/*
+	 * Note: isb() is not required after this direct write
+	 * because there is no indirect read subsequent to it
+	 * (per ARM DDI 0487F.c table D13-1).
+	 */
+	write_sysreg_s(0, SYS_TFSR_EL1);
+
+	return true;
+}
+
+static __always_inline bool mte_get_reset_tfsr(void)
+{
+	/*
+	 * The barriers are required to guarantee that the indirect writes
+	 * to TFSR_EL1 are synchronized before we report the state.
+	 */
+	dsb(nsh);
+	isb();
+
+	return __mte_get_reset_tfsr();
+}
+
 #ifdef CONFIG_ARM64_MTE
 
 /* track which pages have valid allocation tags */
diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 8025ee1f7fdb..47432c9c4de0 100644
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -182,18 +182,8 @@ int mte_enable_kernel_store_only(void)
 #ifdef CONFIG_KASAN_HW_TAGS
 void mte_check_tfsr_el1(void)
 {
-	u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
-
-	if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) {
-		/*
-		 * Note: isb() is not required after this direct write
-		 * because there is no indirect read subsequent to it
-		 * (per ARM DDI 0487F.c table D13-1).
-		 */
-		write_sysreg_s(0, SYS_TFSR_EL1);
-
+	if (__mte_get_reset_tfsr())
 		kasan_report_async();
-	}
 }
 #endif
 

-- 
2.56.0.455.g6c5a503b38-goog