Re: [PATCH RFC v2 15/27] arm64: mte: Check that tag storage blocks are in the same zone

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi,

On Fri, Nov 24, 2023 at 08:56:59PM +0100, David Hildenbrand wrote:
> On 19.11.23 17:57, Alexandru Elisei wrote:
> > alloc_contig_range() requires that the requested pages are in the same
> > zone. Check that this is indeed the case before initializing the tag
> > storage blocks.
> > 
> > Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
> > ---
> >   arch/arm64/kernel/mte_tag_storage.c | 33 +++++++++++++++++++++++++++++
> >   1 file changed, 33 insertions(+)
> > 
> > diff --git a/arch/arm64/kernel/mte_tag_storage.c b/arch/arm64/kernel/mte_tag_storage.c
> > index 8b9bedf7575d..fd63430d4dc0 100644
> > --- a/arch/arm64/kernel/mte_tag_storage.c
> > +++ b/arch/arm64/kernel/mte_tag_storage.c
> > @@ -265,6 +265,35 @@ void __init mte_tag_storage_init(void)
> >   	}
> >   }
> > +/* alloc_contig_range() requires all pages to be in the same zone. */
> > +static int __init mte_tag_storage_check_zone(void)
> > +{
> > +	struct range *tag_range;
> > +	struct zone *zone;
> > +	unsigned long pfn;
> > +	u32 block_size;
> > +	int i, j;
> > +
> > +	for (i = 0; i < num_tag_regions; i++) {
> > +		block_size = tag_regions[i].block_size;
> > +		if (block_size == 1)
> > +			continue;
> > +
> > +		tag_range = &tag_regions[i].tag_range;
> > +		for (pfn = tag_range->start; pfn <= tag_range->end; pfn += block_size) {
> > +			zone = page_zone(pfn_to_page(pfn));
> > +			for (j = 1; j < block_size; j++) {
> > +				if (page_zone(pfn_to_page(pfn + j)) != zone) {
> > +					pr_err("Tag storage block pages in different zones");
> > +					return -EINVAL;
> > +				}
> > +			}
> > +		}
> > +	}
> > +
> > +	 return 0;
> > +}
> > +
> 
> Looks like something that ordinary CMA provides. See cma_activate_area().

Indeed.

> 
> Can't we find a way to let CMA do CMA thingies and only be a user of that?
> What would be required to make the performance issue you spelled out in the
> cover letter be gone and not have to open-code that in arch code?

I've replied with a possible solution here [1].

[1] https://lore.kernel.org/all/ZWSvMYMjFLFZ-abv@raptor/

Thanks,
Alex

> 
> -- 
> Cheers,
> 
> David / dhildenb
>