Re: [RFC PATCH v1 06/38] iommufd: Add and option to request for bar mapping with IORESOURCE_EXCLUSIVE

Jason Gunthorpe
2025-07-29T14:29:19Z

On Tue, Jul 29, 2025 at 01:58:54PM +0530, Aneesh Kumar K.V wrote:
> Jason Gunthorpe <jgg@ziepe.ca> writes:
>
> > On Mon, Jul 28, 2025 at 07:21:43PM +0530, Aneesh Kumar K.V (Arm) wrote:
> >> Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
> >
> > Why would we need this?
> >
> > I can sort of understand why Intel would need it due to their issues
> > with MCE, but ARM shouldn't care either way, should it?
> >
> > But also why is it an iommufd option? That doesn't seem right..
> >
> > Jason
>
> This is based on our previous discussion https://lore.kernel.org/all/20250606120919.GH19710@nvidia.com

I suggested a global option, this is a per-device option, and that
especially seems wrong for iommufd. If it is per-device that is vfio,
if it is global then vfio can pick it up during the early phases of
opening the device.

> IIUC, we intend to request the resource in exclusive mode for secure
> guests—regardless of whether the platform is Intel or ARM. Could you
> help clarify the MCE issue observed on Intel platforms in this context?

As I understand it Intel MCEs if the non-secure side ever reads from
secure'd address space. So there is alot of emphasis there to ensure
there are no CPU mappings.

Jason