arm64: add MTE supported check to thread switching and syscall entry/exit

This lets us avoid doing unnecessary work on hardware that does not
support MTE, and will allow us to freely use MTE instructions in the
code called by mte_thread_switch().

Since this would mean that we do a redundant check in
mte_check_tfsr_el1(), remove it and add two checks now required in its
callers. This also avoids an unnecessary DSB+ISB sequence on the syscall
exit path for hardware not supporting MTE.

Fixes: 392bdd9d4dd7 ("arm64: mte: Enable async tag check fault")
Cc: <stable@vger.kernel.org> # 5.13.x
Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I02fd000d1ef2c86c7d2952a7f099b254ec227a5d
Link: https://lore.kernel.org/r/20210915190336.398390-1-pcc@google.com
[catalin.marinas@arm.com: adjust the commit log slightly]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h
index 3f93b9e0b339b0f808ef1995b73605585e0e3cb0..02511650cffe52188a9696a22ea7cd589421b676 100644 (file)
--- a/arch/arm64/include/asm/mte.h
+++ b/arch/arm64/include/asm/mte.h
@@ -99,11 +99,17 @@ void mte_check_tfsr_el1(void);
 
 static inline void mte_check_tfsr_entry(void)
 {
+       if (!system_supports_mte())
+               return;
+
        mte_check_tfsr_el1();
 }
 
 static inline void mte_check_tfsr_exit(void)
 {
+       if (!system_supports_mte())
+               return;
+
        /*
         * The asynchronous faults are sync'ed automatically with
         * TFSR_EL1 on kernel entry but for exit an explicit dsb()

diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
index 9d314a3bad3ba25fc9e2eedd0eeafecdb11206a3..e5e801bc53122cdb75fa7418827b3a31b9d82eca 100644 (file)
--- a/arch/arm64/kernel/mte.c
+++ b/arch/arm64/kernel/mte.c
@@ -142,12 +142,7 @@ void mte_enable_kernel_async(void)
 #ifdef CONFIG_KASAN_HW_TAGS
 void mte_check_tfsr_el1(void)
 {
-       u64 tfsr_el1;
-
-       if (!system_supports_mte())
-               return;
-
-       tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
+       u64 tfsr_el1 = read_sysreg_s(SYS_TFSR_EL1);
 
        if (unlikely(tfsr_el1 & SYS_TFSR_EL1_TF1)) {
                /*
@@ -199,6 +194,9 @@ void mte_thread_init_user(void)
 
 void mte_thread_switch(struct task_struct *next)
 {
+       if (!system_supports_mte())
+               return;
+
        mte_update_sctlr_user(next);
 
        /*