Re: [PATCH v6 09/14] iommu/vt-d: Add IOMMU_HWPT_ALLOC_PASID support

[Yi Liu <yi.l.liu@intel.com>]

On 2025/2/13 20:56, Jason Gunthorpe wrote:
> On Thu, Feb 13, 2025 at 05:34:52PM +0800, Yi Liu wrote:
>> yes, as iommufd always pin and map user pages for the paging domain, so
>> I don't think there will be any PRIs on S2 due to non-present pages.
> 
> That isn't strictly true, a misbehaving guest could deliberately setup
> a S1 that points to a non-present S2. Ideally this would cause no PRI
> into the guest and the VMM would fault the device.

yes, malicious guest can surely do it.

>> However, PRIs on S2 might occur due to insufficient permissions,
>> potentially caused by userspace. Nonetheless, I am skeptical about the
>> existence of such use cases. What do you think about it?
> 
> I suspect it is "OK", we already have to be safe against a misbehaving
> guest creating a PRI storm, if a misbehaving guest does it via
> pointing to the wrong S2 or just not updating the S1 doesn't seem to
> make much difference..

ok, given these facts, we can consider iommufd does not support valid PRI
on S2 for now. Hence adding the aforementioned enforcement is acceptable.

> IMHO it is desirable for the HW to provide a way to disambiguate the
> PRI.

yes.

Regards,
Yi Liu