Re: [RFC PATCH 05/13] iommufd: Serialise persisted iommufds and ioas

Jason Gunthorpe
2024-10-07T15:01:41Z

On Mon, Oct 07, 2024 at 08:57:07AM +0000, Gowans, James wrote:
> With the ARM SMMUv3 for example I think there are break-before-make
> requirement, so is it possible to do an atomic switch of the SMMUv3 page
> table PGD in a hitless way?

The BBM rules are only about cached translations. If all your IOPTEs
result in the same translation *size* then you are safe. You can
change the radix memory storing the IOPTEs freely, AFAIK.

BBM level 2 capable HW doesn't have those limitations either and
everything is possible.

Jason