Messages in this thread | | | From | "Jason A. Donenfeld" <> | Date | Mon, 25 Jul 2022 00:47:50 +0200 | Subject | Re: [PATCH v3] random: handle archrandom with multiple longs |
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Hey Borislav (or other x86ers),
On Tue, Jul 19, 2022 at 3:02 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote: > > The archrandom interface was originally designed for x86, which supplies > RDRAND/RDSEED for receiving random words into registers, resulting in > one function to generate an int and another to generate a long. However, > other architectures don't follow this. > > On arm64, the SMCCC TRNG interface can return between 1 and 3 longs. On > s390, the CPACF TRNG interface can return arbitrary amounts, with 32 > longs having the same cost as one. On UML, the os_getrandom() interface > can return arbitrary amounts. > > So change the api signature to take a "max_longs" parameter designating > the maximum number of longs requested, and then return the number of > longs generated. > > Since callers need to check this return value and loop anyway, each arch > implementation does not bother implementing its own loop to try again to > fill the maximum number of longs. Additionally, all existing callers > pass in a constant max_longs parameter. Taken together, these two things > mean that the codegen doesn't really change much for one-word-at-a-time > platforms, while performance is greatly improved on platforms such as > s390.
This patch now has acks from Heiko, Catalin, Mark, and Michael, covering the arm, ppc, and s390 changes. The changes to s390 and arm were non-trivial so those acks were quite meaningful. On x86 and ppc, the code compiles down to basically the same assembly and the change really doesn't matter at all. Nonetheless, I thought I should give you a final poke in case you want to ack or nack this, lest I step on the tip.git of your shoes.
Jason
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