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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: linux-efi@vger.kernel.org
Cc: Ard Biesheuvel <ardb@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>
Subject: [PATCH 1/2] efi: Disable runtime services on RT
Date: Fri, 24 Sep 2021 15:49:18 +0200	[thread overview]
Message-ID: <20210924134919.1913476-2-bigeasy@linutronix.de> (raw)
In-Reply-To: <20210924134919.1913476-1-bigeasy@linutronix.de>

Based on measurements the EFI functions get_variable /
get_next_variable take up to 2us which looks okay.
The functions get_time, set_time take around 10ms. These 10ms are too
much. Even one ms would be too much.
Ard mentioned that SetVariable might even trigger larger latencies if
the firmware will erase flash blocks on NOR.

The time-functions are used by efi-rtc and can be triggered during
run-time (either via explicit read/write or ntp sync).

The variable write could be used by pstore.
These functions can be disabled without much of a loss. The poweroff /
reboot hooks may be provided by PSCI.

Disable EFI's runtime wrappers on PREEMPT_RT.

This was observed on "EFI v2.60 by SoftIron Overdrive 1000".

Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 drivers/firmware/efi/efi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 847f33ffc4aed..39031cfcb6b92 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -66,7 +66,7 @@ struct mm_struct efi_mm = {
 
 struct workqueue_struct *efi_rts_wq;
 
-static bool disable_runtime;
+static bool disable_runtime = IS_ENABLED(CONFIG_PREEMPT_RT);
 static int __init setup_noefi(char *arg)
 {
 	disable_runtime = true;
-- 
2.33.0


  reply	other threads:[~2021-09-24 13:49 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-24 13:49 [PATCH 0/2] efi: Disable runtime services on RT Sebastian Andrzej Siewior
2021-09-24 13:49 ` Sebastian Andrzej Siewior [this message]
2021-09-28 13:30   ` [PATCH 1/2] " Ard Biesheuvel
2021-09-28 13:33     ` Sebastian Andrzej Siewior
2021-09-28 13:34       ` Ard Biesheuvel
2021-09-28 14:24         ` Sebastian Andrzej Siewior
2021-10-20  6:09           ` joeyli
2021-10-20  6:28             ` Sebastian Andrzej Siewior
2021-10-20  6:47               ` joeyli
2021-10-20  7:20                 ` Sebastian Andrzej Siewior
2021-09-28 20:28         ` Thomas Gleixner
2021-09-28 20:41           ` Ard Biesheuvel
2021-09-24 13:49 ` [PATCH 2/2] efi: Allow efi=runtime Sebastian Andrzej Siewior

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