From c88c78c2d2d372ea3c0672323ef4214edeb3fdb6 Mon Sep 17 00:00:00 2001 From: Peter Collingbourne Date: Tue, 17 Nov 2020 19:20:51 -0800 Subject: [PATCH] UPSTREAM: arm64: mte: optimize asynchronous tag check fault flag check [ Upstream commit 739003c6428387432d42b9b80be185cde93978aa ] We don't need to check for MTE support before checking the flag because it can only be set if the hardware supports MTE. As a result we can unconditionally check the flag bit which is expected to be in a register and therefore the check can be done in a single instruction instead of first needing to load the hwcaps. On a DragonBoard 845c with a kernel built with CONFIG_ARM64_MTE=y with the powersave governor this reduces the cost of a kernel entry/exit (invalid syscall) from 465.1ns to 463.8ns. Signed-off-by: Peter Collingbourne Link: https://lore.kernel.org/r/20201118032051.1405907-1-pcc@google.com [catalin.marinas@arm.com: remove IS_ENABLED(CONFIG_ARM64_MTE)] Signed-off-by: Catalin Marinas Bug: 172318110 Signed-off-by: Andrey Konovalov Change-Id: Ifed200a8614e4c790cae1c7471439b12b4d4f8a0 --- arch/arm64/kernel/syscall.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm64/kernel/syscall.c b/arch/arm64/kernel/syscall.c index f8f758e4a306..f61e9d8cc55a 100644 --- a/arch/arm64/kernel/syscall.c +++ b/arch/arm64/kernel/syscall.c @@ -122,7 +122,7 @@ static void el0_svc_common(struct pt_regs *regs, int scno, int sc_nr, cortex_a76_erratum_1463225_svc_handler(); local_daif_restore(DAIF_PROCCTX); - if (system_supports_mte() && (flags & _TIF_MTE_ASYNC_FAULT)) { + if (flags & _TIF_MTE_ASYNC_FAULT) { /* * Process the asynchronous tag check fault before the actual * syscall. do_notify_resume() will send a signal to userspace