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

["Alex Bennée" <alex.bennee@linaro.org>]

Dave Martin <Dave.Martin@arm.com> writes:

> 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.

We shall see how far I get tomorrow - you won't get any more from me
after that until I get back from holiday so don't delay v2 on my account
;-)

>
> Cheers
> ---Dave