Re: [PATCH] iommu/amd: Add kernel parameters to limit V1 page-sizes

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Sep 05, 2024 at 02:52:06PM -0300, Jason Gunthorpe wrote:
> On Thu, Sep 05, 2024 at 05:13:53PM +0200, Joerg Roedel wrote:
> > On Thu, Sep 05, 2024 at 09:05:31AM -0300, Jason Gunthorpe wrote:
> > > On Thu, Sep 05, 2024 at 09:34:07AM +0200, Joerg Roedel wrote:
> > > > On Thu, Sep 05, 2024 at 03:31:08PM +0800, Baolu Lu wrote:
> > > > > "iommu.nohugepages=1"?
> > > > 
> > > > Generally yes, but that requires to touch all drivers to make the
> > > > behavior consistent. We can start this effort on-top of this change, if
> > > > desired.
> > > 
> > > Let's at least use the same keyword that already exists though??
> > 
> > You mean amd_iommu=sp_off? I am not in favour of that, in the Linux
> > world the term 'hugepage' is more common than 'superpage'. So I
> > would avoid spreading the use of the later. We can extend that later to
> > the iommu.nohugepages parameter suggested by Baolu.
> 
> I see, okay, let me check with some people if the mlx5 part is Ok

Apparently we have cases that rely on some other single page sizes (eg
like 64G or something), a bitmap would probably be better. There was an
ask that this apply to Intel as well.

So, I think this would be better to start as a generic iommu parameter
with a bitmap, and do the pagesize fixing in the core code, after
domains are allocated, instead of in the AMD driver.

Jason