Re: [PATCH] iommu/arm-smmu-v3: Add HAFT support for SVA

On 22/07/2026 2:24 pm, Will Deacon wrote:
> On Wed, Jul 01, 2026 at 06:45:17PM +0100, Robin Murphy wrote:
>> Since table access flags cannot be software-managed, if process
>> pagetables are using HAFT then SVA must require the SMMU to support and
>> enable it too, otherwise page aging is liable to get out of whack.
>>
>> Cc: <[email protected]>
>> Fixes: 62df5870ebf7 ("arm64: Enable ARCH_HAS_NONLEAF_PMD_YOUNG")
>> Signed-off-by: Robin Murphy <[email protected]>
>> ---
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 5 +++++
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c     | 6 ++++++
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h     | 3 +++
>>   3 files changed, 14 insertions(+)
> 
> This looks ok to *me*, but Sashiko raises two interesting points:
> 
> https://sashiko.dev/#/patchset/878cd6bcbbe2d5677d2f63da13294c148268552c.1782927917.git.robin.murphy@arm.com
> 
> 1. This may break hitless updates when transitioning to a faulting entry.

What does that even mean? We might block traffic in the process of 
_explicitly blocking traffic_!? Whoop-de-do, surely?

But either way, HAFT has bog all to do with EPD0, and it must be cleared 
if HA is cleared, otherwise the CD becomes illegal.

> 2. IORT has HTTU overrides for HA/HD. Does it (will it?) have anything
>     for HAFT? At the moment, it looks like you'll trigger a warning
>     message.

Oh, seems I did miss that fiddly fw_features line, so I guess it has 
half a point that the warning can wonky if both IDR0 and IORT do 
(correctly) report HAFT. Pretty sure we're already a bit broken if IORT 
ever did try to override HTTU _upwards_, though.

> Given Jason's comments, it's probably worth sending the idreg override
> patch as well...

Fair enough, I'm blessed with a moment of calm just now so I should be 
able to find time to have a crack at that tomorrow...

Cheers,
Robin.