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

[Mario Limonciello <superm1@kernel.org>]

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@ziepe.ca>
>> Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
>> ---
>> 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.