On Tue, Jul 19, 2022 at 03:02:07PM +0200, Jason A. Donenfeld 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. > > Cc: Will Deacon <will@xxxxxxxxxx> > Cc: Alexander Gordeev <agordeev@xxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: H. Peter Anvin <hpa@xxxxxxxxx> > Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxx> > Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> > Cc: Johannes Berg <johannes@xxxxxxxxxxxxxxxx> > Cc: Mark Rutland <mark.rutland@xxxxxxx> > Cc: Harald Freudenberger <freude@xxxxxxxxxxxxx> > Acked-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx> > Signed-off-by: Jason A. Donenfeld <Jason@xxxxxxxxx> For arm64: Acked-by: Catalin Marinas <catalin.marinas@xxxxxxx>
