This is a note to let you know that I've just added the patch titled
random: avoid reading two cache lines on irq randomness
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
random-avoid-reading-two-cache-lines-on-irq-randomness.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 9ee0507e896b45af6d65408c77815800bce30008 Mon Sep 17 00:00:00 2001
From: "Jason A. Donenfeld" <Jason@xxxxxxxxx>
Date: Thu, 22 Sep 2022 18:46:04 +0200
Subject: random: avoid reading two cache lines on irq randomness
From: Jason A. Donenfeld <Jason@xxxxxxxxx>
commit 9ee0507e896b45af6d65408c77815800bce30008 upstream.
In order to avoid reading and dirtying two cache lines on every IRQ,
move the work_struct to the bottom of the fast_pool struct. add_
interrupt_randomness() always touches .pool and .count, which are
currently split, because .mix pushes everything down. Instead, move .mix
to the bottom, so that .pool and .count are always in the first cache
line, since .mix is only accessed when the pool is full.
Fixes: 58340f8e952b ("random: defer fast pool mixing to worker")
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/char/random.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -891,10 +891,10 @@ void __init add_bootloader_randomness(co
}
struct fast_pool {
- struct work_struct mix;
unsigned long pool[4];
unsigned long last;
unsigned int count;
+ struct work_struct mix;
};
static DEFINE_PER_CPU(struct fast_pool, irq_randomness) = {
Patches currently in stable-queue which might be from Jason@xxxxxxxxx are
queue-4.9/random-avoid-reading-two-cache-lines-on-irq-randomness.patch
queue-4.9/random-clamp-credited-irq-bits-to-maximum-mixed.patch
