From: Peter Collingbourne pcc@google.com

commit 8c8a3b5bd960cd88f7655b5251dc28741e11f139 upstream.

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: 65812c6921cc ("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/I02fd000d1ef2c86c7d2952a7f099b254ec... 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 --- arch/arm64/include/asm/mte.h | 6 ++++++ arch/arm64/kernel/mte.c | 10 ++++------ 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/include/asm/mte.h b/arch/arm64/include/asm/mte.h index 58c7f80f5596..c724a288a412 100644 --- a/arch/arm64/include/asm/mte.h +++ b/arch/arm64/include/asm/mte.h @@ -105,11 +105,17 @@ 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 36f51b0e438a..d223df11fc00 100644 --- a/arch/arm64/kernel/mte.c +++ b/arch/arm64/kernel/mte.c @@ -173,12 +173,7 @@ bool mte_report_once(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)) { /* @@ -221,6 +216,9 @@ void mte_thread_init_user(void)

void mte_thread_switch(struct task_struct *next) { + if (!system_supports_mte()) + return; + /* * Check if an async tag exception occurred at EL1. *