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UPSTREAM: arm64: mte: optimize asynchronous tag check fault flag check

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[ Upstream commit 739003c642 ]

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 <pcc@google.com>
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 <catalin.marinas@arm.com>
Bug: 172318110
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Change-Id: Ifed200a8614e4c790cae1c7471439b12b4d4f8a0
This commit is contained in:
Peter Collingbourne
2020-11-17 19:20:51 -08:00
committed by Alistair Delva
parent 6a361ab4ec
commit c88c78c2d2
1 changed files with 1 additions and 1 deletions
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2
arch/arm64/kernel/syscall.c
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@@ -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