Re: [PATCH v4] iommu/amd: Make PerfOpt compulsory

[Mario Limonciello]

On 10/1/26 10:44 PM, Vasant Hegde wrote:
> On 10/1/2026 11:54 PM, Mario Limonciello (AMD) wrote:
> > PerfOpt is only a feature usable by integrated GPUs and only in identity
> > mode.  Instead of leaving a policy knob in amdgpu, just turn it on when
> > an integrated GPU is in identity.
> >
> > PerfOpt locks the GPU into identity mode where the DTE is ignored, so mark
> > it require_direct (blocks VFIO/iommufd claims) and disable PASID (no GCR3
> > table in the fast path).
> >
> > This drops quite a bit of compatibility glue.  There was a refcounting
> > system, exported symbols, and device attach/detach logic.  By just setting
> > it immediately it's a lot more straightforward.
> >
> > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxx>
> > Signed-off-by: Mario Limonciello (AMD) <superm1@xxxxxxxxxx>
> > ---
> > v4:
> >   * Disable PASID for PerfOpt devices
> >   * Don't allow attaching a blocked domain
>
> This will block attaching device to guest via vfio-pci. Is that fine?
>
> -Vasant

Right - The thing is from that experiment on v3, putting it in blocked 
domain does nothing while PerfOpt is enabled.

I figured the user should be aware; so I was between blocking attaching 
a blocked domain or showing a warning.