Re: Cache Invalidation Solution for Nested IOMMU

[Nicolin Chen <nicolinc@nvidia.com>]

On Wed, May 03, 2023 at 03:14:28PM +0000, Shameerali Kolothum Thodi wrote:

> > > On my emulation environment (very slow), with mmap, I see
> > > improvements. I'll also try setting up a test suite on a proper HW
> > > this week.
> > >
> >
> > Still debugging the mmap method here,
> >
> > Status 4.12
> >
> > 1.  ioctl method works, based on iommufd
 
> I had a go with your above branches. The issue below seems to happen only
> when you assign multiple devices to Guest. It looks like when you have multiple devices
> attached to Guest, the host kernel receives invalid Guest cmd(0x0) and ends up issuing
> that to HW triggering the below errors.

I actually found a bug in my previous wip branch (non-mmap),
resulting in a cons/prod index overflow. But the mmap branch
seems to be okay, since my QEMU code copies all TLBI commands
starting from index=0x0.

You may compare the git-diff, just in case that it helps:
https://github.com/nicolinc/iommufd/commits/wip/iommufd_nesting-04262023-Nic
https://github.com/nicolinc/qemu/commits/wip/iommufd_nesting-04222023

Btw, I ran a comparison on a real hardware. But it does not
show significant improvements between the ioctl solution and
the mmap solution. So I kept the ioctl one in v2.

Thanks
Nic