Re: About unmap pages and set dirty tracking on nested parent domain

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jan 25, 2024 at 10:03:31AM -0400, Jason Gunthorpe wrote:
> On Thu, Jan 25, 2024 at 09:55:46PM +0800, Yi Liu wrote:
> > Hi Jason, Kevin,
> > 
> > Today, Intel iommu driver only tracks attached devices/iommus in the nested
> > domain. While the nested parent domain does not.
> 
> Heh, I was just looking at this bug on my ARM implemention too :)

What I did for SMMU is on my github how:

https://github.com/jgunthorpe/linux/commits/smmuv3_newapi/

See iommu/arm-smmu-v3: Support IOMMU_DOMAIN_NESTED

The list that tracks where the iommu domain sends its invalidations
gets a flag indicating that ATC has to be a full flush

The domain gets a flag that says the IOTLB has to be a full flush (to
wipe the nest child entries too)

Also note that if the VM is being relied on to generate ATC
invalidations then the hypervisor must also track the VM's ATS
state. If the VM thinks ATS is off then it will not issue ATC flushes.

ARM has a convenient STE bit that makes this simple, otherwise the VMM
will have to trap the PCI-E ATS config write and forward it through
iommufd somehow.

Tracking all the ATS stuff was a big PITA, I think the approach I got
for SMMU is pretty good though.

Jason