From: David Laight <David.Laight@ACULAB.COM>
To: 'Christophe Leroy' <christophe.leroy@csgroup.eu>,
"Jason A. Donenfeld" <Jason@zx2c4.com>
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Subject: RE: [PATCH v3 3/5] treewide: use get_random_u32() when possible
Date: Fri, 7 Oct 2022 09:14:54 +0000 [thread overview]
Message-ID: <e0c127f9e80146c19fab9f987bb2f588@AcuMS.aculab.com> (raw)
In-Reply-To: <6396875c-146a-acf5-dd9e-7f93ba1b4bc3@csgroup.eu>
From: Christophe Leroy
> Sent: 06 October 2022 18:43
...
> But taking into account that sp must remain 16 bytes aligned, would it
> be better to do something like ?
>
> sp -= prandom_u32_max(PAGE_SIZE >> 4) << 4;
That makes me think...
If prandom_u32_max() is passed a (constant) power of 2 it doesn't
need to do the multiply, it can just do a shift right.
Doesn't it also always get a 32bit random value?
So actually get_random_u32() & PAGE_MASK & ~0xf is faster!
When PAGE_SIZE is 4k, PAGE_SIZE >> 4 is 256 so it could use:
get_ramdom_u8() << 4
You also seem to have removed prandom_u32() in favour of
get_random_u32() but have added more prandom_xxxx() functions.
David
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Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
next prev parent reply other threads:[~2022-10-07 9:15 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-06 16:53 [PATCH v3 0/5] treewide cleanup of random integer usage Jason A. Donenfeld
2022-10-06 16:53 ` [PATCH v3 1/5] treewide: use prandom_u32_max() when possible Jason A. Donenfeld
2022-10-06 16:53 ` [PATCH v3 2/5] treewide: use get_random_{u8,u16}() " Jason A. Donenfeld
2022-10-06 16:53 ` [PATCH v3 3/5] treewide: use get_random_u32() " Jason A. Donenfeld
2022-10-06 17:21 ` Christophe Leroy
2022-10-06 17:24 ` Jason A. Donenfeld
2022-10-06 17:31 ` Christophe Leroy
2022-10-06 17:42 ` Christophe Leroy
2022-10-06 23:36 ` Jason A. Donenfeld
2022-10-07 4:57 ` Christophe Leroy
2022-10-07 14:07 ` Jason A. Donenfeld
2022-10-07 17:12 ` Kees Cook
2022-10-07 17:56 ` Jason A. Donenfeld
2022-10-08 21:53 ` David Laight
2022-10-09 2:57 ` Jason A. Donenfeld
2022-10-07 9:14 ` David Laight [this message]
2022-10-07 9:26 ` Mika Westerberg
2022-10-06 16:53 ` [PATCH v3 4/5] treewide: use get_random_bytes " Jason A. Donenfeld
2022-10-06 17:22 ` Christophe Leroy
2022-10-07 3:09 ` Bagas Sanjaya
2022-10-07 3:23 ` Jason A. Donenfeld
2022-10-06 16:53 ` [PATCH v3 5/5] prandom: remove unused functions Jason A. Donenfeld
2022-10-07 9:11 ` [PATCH v3 0/5] treewide cleanup of random integer usage Ulf Hansson
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