Re: [RFC PATCH 0/5] iommu/arm-smmu-v3: Implement Runtime/System Sleep ops

[Jason Gunthorpe <jgg@ziepe.ca>]

On Thu, Mar 20, 2025 at 10:28:44PM +0000, Mostafa Saleh wrote:
> On Wed, Mar 19, 2025 at 04:46:09PM -0300, Jason Gunthorpe wrote:
> > On Wed, Mar 19, 2025 at 06:22:30PM +0000, Robin Murphy wrote:
> > > I don't see SVA and VFIO needing any special considerations, so it might
> > > just be the new vIOMMU stuff which may need to hold PM enabled for the
> > > lifetime of things exposed to userspace.
> > 
> > Are you expecting that the VFIO driver, and whatever driver is
> > managing the SVA will keep the power turned on as necessary then?
> > 
> > VFIO is not going to work if the SMMU power goes off unexpectedly
> > while the VFIO FD is open.
> > 
> > I suppose VFIO also can power off on-demand via userspace asking
> > it. In that case the VM would be co-operating.
> 
> I guess VFIO is tricky as there is a security boundary. In case the
> SMMUv3 wakes up with caches not clean, there is a window of time where
> the device is accessible from userspace with old (or garbage) TLBs.
> I see VFIO-platform always take a PM reference for the device at
> open(), but I am not sure how that works with VFIO-pci.

I think that is my prior remark, PM must either abort or translate
exactly as the domain contains. Never something weird/old/bypass.

If the HW isn't guaranteeing that then we have a bigger discussion
here about how to deal with the security issues that creates.

Jason