> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Friday, February 3, 2023 11:04 PM
> 
> On Fri, Feb 03, 2023 at 08:09:30AM +0000, Tian, Kevin wrote:
> > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > Sent: Thursday, February 2, 2023 3:05 PM
> > >
> > > QEMU with this feature should have the vIOMMU maintain a cache of the
> > > guest io page table addresses and assign a unique IOAS to each unique
> > > guest page table.
> >
> > I didn't get why we impose such requirement to userspace.
> 
> I read this as implementation guidance for qemu. qemu can do what it
> wants of course
> 

sure but I still didn't get why this is a guidance specific to the
new replace cmd...

On Mon, Feb 06, 2023 at 06:39:29AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Friday, February 3, 2023 11:04 PM
> > 
> > On Fri, Feb 03, 2023 at 08:09:30AM +0000, Tian, Kevin wrote:
> > > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > > Sent: Thursday, February 2, 2023 3:05 PM
> > > >
> > > > QEMU with this feature should have the vIOMMU maintain a cache of the
> > > > guest io page table addresses and assign a unique IOAS to each unique
> > > > guest page table.
> > >
> > > I didn't get why we impose such requirement to userspace.
> > 
> > I read this as implementation guidance for qemu. qemu can do what it
> > wants of course
> > 
> 
> sure but I still didn't get why this is a guidance specific to the
> new replace cmd...

I think the guidance is about the change to VFIO uAPI where it is now
possible to change the domain attached, previously that was not
possible

Jason

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Monday, February 6, 2023 9:26 PM
> 
> On Mon, Feb 06, 2023 at 06:39:29AM +0000, Tian, Kevin wrote:
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Friday, February 3, 2023 11:04 PM
> > >
> > > On Fri, Feb 03, 2023 at 08:09:30AM +0000, Tian, Kevin wrote:
> > > > > From: Nicolin Chen <nicolinc@nvidia.com>
> > > > > Sent: Thursday, February 2, 2023 3:05 PM
> > > > >
> > > > > QEMU with this feature should have the vIOMMU maintain a cache of
> the
> > > > > guest io page table addresses and assign a unique IOAS to each
> unique
> > > > > guest page table.
> > > >
> > > > I didn't get why we impose such requirement to userspace.
> > >
> > > I read this as implementation guidance for qemu. qemu can do what it
> > > wants of course
> > >
> >
> > sure but I still didn't get why this is a guidance specific to the
> > new replace cmd...
> 
> I think the guidance is about the change to VFIO uAPI where it is now
> possible to change the domain attached, previously that was not
> possible
> 

that is fine. I just didn't get why the original description emphasized
the cache and unique IOAS aspects in Qemu.