Re: [RFC PATCH v2 4/4] arm64: Export id_aar64fpr0 via sysfs

Qais Yousef
2020-10-21T13:22:30Z

On 10/21/20 13:15, Catalin Marinas wrote:
> On Wed, Oct 21, 2020 at 12:09:58PM +0100, Marc Zyngier wrote:
> > On 2020-10-21 11:46, Qais Yousef wrote:
> > > Example output. I was surprised that the 2nd field (bits[7:4]) is
> > > printed out
> > > although it's set as FTR_HIDDEN.

^^^^^^^^^

> > > # cat /sys/devices/system/cpu/cpu*/regs/identification/id_aa64pfr0
> > > 0x0000000000000011
> > > 0x0000000000000011
> > > 0x0000000000000011
> > > 0x0000000000000011
> > > 0x0000000000000011
> > > 0x0000000000000011
> > >
> > > # echo 1 > /proc/sys/kernel/enable_asym_32bit
> > >
> > > # cat /sys/devices/system/cpu/cpu*/regs/identification/id_aa64pfr0
> > > 0x0000000000000011
> > > 0x0000000000000011
> > > 0x0000000000000012
> > > 0x0000000000000012
> > > 0x0000000000000011
> > > 0x0000000000000011
> >
> > This looks like a terrible userspace interface. It exposes unrelated
> > features,
>
> Not sure why the EL1 field ended up in here, that's not relevant to the
> user.

I was surprised by this too. Not sure a bug at my end or a bug in the way
arm64_ftr_reg stores reg->user_val and reg->user_mask.

FWIW, I did highlight the problem above.

It is something to fix indeed.

Thanks

--
Qais Yousef