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

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Date:   Thu, 30 Nov 2023 12:00:11 +0000
From:   Alexandru Elisei <alexandru.elisei@....com>
To:     Hyesoo Yu <hyesoo.yu@...sung.com>
Cc:     catalin.marinas@....com, will@...nel.org, oliver.upton@...ux.dev,
        maz@...nel.org, james.morse@....com, suzuki.poulose@....com,
        yuzenghui@...wei.com, arnd@...db.de, akpm@...ux-foundation.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com, mhiramat@...nel.org,
        rppt@...nel.org, hughd@...gle.com, pcc@...gle.com,
        steven.price@....com, anshuman.khandual@....com,
        vincenzo.frascino@....com, david@...hat.com, eugenis@...gle.com,
        kcc@...gle.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kvmarm@...ts.linux.dev,
        linux-fsdevel@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 15/27] arm64: mte: Check that tag storage blocks
 are in the same zone

Hi,

On Wed, Nov 29, 2023 at 05:57:44PM +0900, Hyesoo Yu wrote:
> On Sun, Nov 19, 2023 at 04:57:09PM +0000, 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@....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));
> 
> Hello.
> 
> Since the blocks within the tag_range must all be in the same zone, can we move the "page_zone"
> out of the loop ?

Hmm.. why do you say that the pages in a tag_range must be in the same
zone? I am not very familiar with how the memory management code puts pages
into zones, but I would imagine that pages in a tag range straddling the
4GB limit (so, let's say, from 3GB to 5GB) will end up in both ZONE_DMA and
ZONE_NORMAL.

Thanks,
Alex

> 
> Thanks,
> Regards.
> 
> > +			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;
> > +}
> > +
> >  static int __init mte_tag_storage_activate_regions(void)
> >  {
> >  	phys_addr_t dram_start, dram_end;
> > @@ -321,6 +350,10 @@ static int __init mte_tag_storage_activate_regions(void)
> >  		goto out_disabled;
> >  	}
> >  
> > +	ret = mte_tag_storage_check_zone();
> > +	if (ret)
> > +		goto out_disabled;
> > +
> >  	for (i = 0; i < num_tag_regions; i++) {
> >  		tag_range = &tag_regions[i].tag_range;
> >  		for (pfn = tag_range->start; pfn <= tag_range->end; pfn += pageblock_nr_pages)
> > -- 
> > 2.42.1
> > 
> >