Re: [PATCH v3 1/2] iommu/amd: Remove PT_FEAT_DYNAMIC_TOP from PT_FORCE_ENABLED_FEATURES

[Ankit Soni]

On Thu, Mar 12, 2026 at 08:22:23AM -0300, Jason Gunthorpe wrote:
> On Thu, Mar 12, 2026 at 04:10:13AM +0000, Ankit Soni wrote:
> > On Wed, Mar 11, 2026 at 01:44:03PM -0300, Jason Gunthorpe wrote:
> > > On Wed, Mar 11, 2026 at 09:54:55PM +0530, Vasant Hegde wrote:
> > > > 
> > > > + Jason
> > > > 
> > > > On 3/9/2026 7:35 PM, Ankit Soni wrote:
> > > > > Dynamic top is used to grow the page table levels. However, if the VA
> > > > > size is small and the initial page table level already covers the entire
> > > > > address space, table growth is not required. In that case, the generic
> > > > > page table framework clears PT_FEAT_DYNAMIC_TOP, which in turn causes
> > > > > error -EOPNOTSUPP and leads to domain initialization failure.
> > > > > 
> > > > > Remove PT_FEAT_DYNAMIC_TOP from PT_FORCE_ENABLED_FEATURES, since during
> > > > > domain allocation AMD IOMMU driver explicitly sets PT_FEAT_DYNAMIC_TOP
> > > > > via cfg.common.features, this keeps normal runtime behavior unchanged.
> > > > > 
> > > > 
> > > > Fixes: 879ced2bab1 ("iommupt: Add the AMD IOMMU v1 page table format")
> > > 
> > > No.. There is no bug here.
> > > 
> > > I don't really understand why you'd want to do this, the driver still
> > > sets PT_FEAT_DYNAMIC_TOP, so what is the issue?
> > > 
> > > It shouldn't be removed from PT_FORCE_ENABLED_FEATURES, something else
> > > is wrong.
> > > 
> > > Jason
> > 
> > When hw_max_vasz_lg2 = 32 and starting_level = 2, top_range.max_vasz_lg2
> > comes back as 32 (clamped by min(32, 39)), so it matches
> > common->max_vasz_lg2. The 'pt_init_common()' clears dynamic top because 
> > "the table can't grow beyond its current level." with next condition in
> > this function, domain init will fail with "-EOPNOTSUPP".
> 
> Ok, that is much clearer, but this is not the way to fix it.
> 
> First it needs test coverage added
> 
> And probably we should remove that if but it should be checked closely.
> 
> Jason

Thanks for the heads‑up. I’ll add the test coverage and the other changes
separately.

-Ankit