Re: [PATCH v2 4/4] iommu/arm: Add BBM Level 2 smmu feature

[Jason Gunthorpe]

On Tue, Mar 04, 2025 at 04:02:20PM +0000, Ryan Roberts wrote:
> On 04/03/2025 14:26, Jason Gunthorpe wrote:
> > On Mon, Mar 03, 2025 at 07:03:42PM +0000, Mikołaj Lenczewski wrote:
> > 
> >> For example, if we use BBML2 for kernel mappings, does that require us
> >> to repaint all kernel mappings when disabling BBML2 on smmu attach? I
> >> am not sure, but definitely something to be worked out.
> > 
> > No, it would be a per-mm_struct basis only if we did something like
> > that
> > 
> > When the SMMU driver puts a SVA on top of the mm_struct it would
> > disable BBML2 usage only for that mm_struct and it's contained VMAs.
> 
> I guess we would need to figure out some synchonization mechanism if disabling
> BBML2 dynaically per-mm. If there was already a BBML2 operation in flight would
> want to wait for it to end. But that's a problem to solve if/when it's shown to
> be needed, I think.

I have a feeling we can piggyback on the mmu notifiers to achieve this
as all the changes to the PTEs should be bracketed by notifier
callbacks..

Let's hope it isn't needed.

Jasob