Re: [PATCH 11/27] arm64/sve: Core task context handling

Dave Martin
2017-08-22T17:19:59Z

On Tue, Aug 22, 2017 at 05:21:19PM +0100, Alex Bennée wrote:
>
> Dave Martin <Dave.Martin@arm.com> writes:

[...]

> > --- a/arch/arm64/include/asm/processor.h
> > +++ b/arch/arm64/include/asm/processor.h
> > @@ -85,6 +85,8 @@ struct thread_struct {
> > unsigned long tp2_value;
> > #endif
> > struct fpsimd_state fpsimd_state;
> > + void *sve_state; /* SVE registers, if any */
> > + u16 sve_vl; /* SVE vector length */
>
> sve_vl is implicitly cast to unsigned int bellow - it should be
> consistent.

Agreed -- I think this can just be unsigned int here, which is the type
I use everywhere except when encoding the vector length in the signal
frame and ptrace data.

During development, there was an additional flags field here (now
merged into the thread_info flags). u16 was big enough for the largest
architectural vector length, so it seemed "tidy" to make both u16s.
Elsewhere, this created a risk of overflow if you try to compute say
the size of the whole register file from a u16, so I generally used
unsigned int for local variables in functions that handle the vl.

> Given the allocation functions rely on sve_vl being valid it might be
> worth noting where this is set/live from?

Agreed, I need to look more closely at exactly how to justify the
soundness of this in order to thin out BUG_ONs.

If you need any pointers, please ping me. In the meantime, I would
rather not colour your judgement by infecting you with my assumptions ;)

> > unsigned long fault_address; /* fault info */
> > unsigned long fault_code; /* ESR_EL1 value */
> > struct debug_info debug; /* debugging */
> > diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> > index 46c3b93..1a4b30b 100644
> > --- a/arch/arm64/include/asm/thread_info.h
> > +++ b/arch/arm64/include/asm/thread_info.h
> <snip>
>
> And I see there are other comments from Ard.

Yup, I've already picked those up.

I'll be posting a v2 with feedback applied once I've reviewed the
existing BUG_ON()s -- should happen sometime this week.

Cheers
---Dave