Re: [PATCH v3 07/17] iommufd: Add IOMMU_RESV_IOVA_RANGES

[Jason Gunthorpe]

On Wed, Aug 02, 2023 at 01:09:28AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > Sent: Wednesday, August 2, 2023 2:23 AM
> > 
> > On Tue, Aug 01, 2023 at 02:40:44AM +0000, Tian, Kevin wrote:
> > 
> > > > So, I guess we should leave it like this?
> > > >
> > >
> > > Yes. Along with this discussion (including what you explained for sw_msi)
> > > let's abandon this new cmd and leave it as today.
> > 
> > You sure? This makes it basically impossible to write a "correct" vmm
> > that is aware of what the physical memory map must be early on
> > 
> 
> emmm... I thought it's what you meant by "leave it like this" and the
> fact that existing VMM's memory layout happens to match the reserved
> regions. Nobody complains lacking of such a interface for years then
> we may postpone supporting it until it's really required.
> 
> btw even if we add this new cmd now, getting the Qemu support to
> use the aggregated list when creating the guest memory map is not
> a simple task given currently vfio only passively acts on change
> notifications in the guest memory layout. It requires a new mechanism
> to enforce strict order (probe all vfio devices before creating the memory
> layout) and then injects vfio reserved regions into the layout.
> 
> Preferably let's not making it a hard dependency for this series.

I see, if qemu won't use it then lets not do it

Jason