Re: [PATCH v2] random: handle archrandom in plural words

Gabriel Paubert
2022-07-18T06:55:26Z

On Mon, Jul 18, 2022 at 04:31:11PM +1000, Michael Ellerman wrote:
> "Jason A. Donenfeld" <Jason@zx2c4.com> writes:
> > 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 words. On
> > s390, the CPACF TRNG interface can return between 1 and 32 words for the
> > same cost as for one word. On UML, the os_getrandom() interface can return
> > arbitrary amounts.
> >
> > So change the api signature to take a "words" parameter designating the
> > maximum number of words requested, and then return the number of words
> > generated.
>
> On powerpc a word is 32-bits and a doubleword is 64-bits (at least
> according to the ISA). I think that's also true on other 64-bit
> architectures.

IIRC, this is (or was) not the case on Alpha, where word was defined as
16 bits. All assembly mnemonics had w for 16 bits, l for 32 bits, and q
for 64 bits.

Blame the PDP-11...

Gabriel

>
> You could avoid any confusion by defining the API in terms of "longs"
> rather than "words".
>
> But that's just a comment, see what others think.
>
> > arch/powerpc/include/asm/archrandom.h | 30 ++------
> > arch/powerpc/kvm/book3s_hv.c | 2 +-
>
> Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
>
> cheers