Re: [PATCH 1/3] iommu/io-pgtable-arm: Add nents_per_pgtable in struct io_pgtable_cfg

[Nicolin Chen]

On Fri, Sep 01, 2023 at 07:02:19PM +0100, Robin Murphy wrote:

> > Our test team encountered a soft lockup in this path today:
> > --------------------------------------------------------------------
> > watchdog: BUG: soft lockup - CPU#244 stuck for 26s!
> 
> That's a lot of TLBIs!

Well, imagining the use cases of NVIDIA Grace, I'd expect it soon
to be no longer a surprise that we see more stressful cases :-/

> > I think it is the same problem that we fixed in tlbflush.h using
> > MAX_TLBI_OPS. So, I plan to send a cleaner bug fix (cc stable)

> > What do you think about it?
> 
> Looks reasonable to me - I think it's the right shape to foreshadow the
> bigger refactoring we discussed, 

Cool! Thanks for the quick ack. And I could move the MAX_TLBI_OPS
to the SMMU header so a later change in smmu.c can just use it.

> and I can't object to using
> PAGE_{SIZE,SHIFT} for the calculation when it's specifically in the
> context of SVA.

Yea, the current SVA code passes in PAGE_SIZE as the TLBI granule.

Thanks
Nic