Hi Jacob, > From: Jacob Pan [mailto:jacob.jun.pan@xxxxxxxxxxxxxxx] > Sent: Saturday, February 8, 2020 3:44 AM > To: Liu, Yi L <yi.l.liu@xxxxxxxxx> > Subject: Re: [RFC v3 2/8] vfio/type1: Make per-application (VM) PASID quota tunable > > On Wed, 29 Jan 2020 04:11:46 -0800 > "Liu, Yi L" <yi.l.liu@xxxxxxxxx> wrote: > > > From: Liu Yi L <yi.l.liu@xxxxxxxxx> > > > > The PASID quota is per-application (VM) according to vfio's PASID > > management rule. For better flexibility, quota shall be user tunable > > . This patch provides a VFIO based user interface for which quota can > > be adjusted. However, quota cannot be adjusted downward below the > > number of outstanding PASIDs. > > > > This patch only makes the per-VM PASID quota tunable. While for the > > way to tune the default PASID quota, it may require a new vfio module > > option or other way. This may be another patchset in future. > > > One issue we need to solve is how to share PASIDs at the system > level, e.g. Both VMs and baremetal drivers could use PASIDs. > > This patch is granting quota to a guest w/o knowing the remaining > system capacity. So guest PASID allocation could fail even within its > quota. that's true. > The solution I am thinking is to enforce quota at IOASID common > code, since IOASID APIs already used to manage system-wide allocation. > How about the following changes to IOASID? > 1. introduce quota in ioasid_set (could have a soft limit for better > sharing) > > 2. introduce an API to create a set with quota before allocation, e.g. > ioasid_set_id = ioasid_alloc_set(size, token) > set_id will be used for ioasid_alloc() instead of token. Is the token the mm pointer? I guess you may want to add one more API like ioasid_get_set_id(token), thus that other ioasid user could get set_id with their token. If token is the same give them the same set_id. > > 3. introduce API to adjust set quota ioasid_adjust_set_size(set_id, > size) > > 4. API to check remaining PASIDs ioasid_get_capacity(set_id); //return > system capacity if set_id == 0; > > 5. API to set system capacity, ioasid_set_capacity(nr_pasids), e.g. if > system has 20 bit PASIDs, IOMMU driver needs to call > ioasid_set_capacity(1<<20) during boot. yes, this is definitely necessary. > 6. Optional set level APIs. e.g. ioasid_free_set(set_id), frees all > IOASIDs in the set. If this is provided. I think VFIO may be not necessary to track allocated PASIDs. When VM is down or crashed, VFIO just use this API to reclaim allocated PASIDs. > With these APIs, this patch could query PASID capacity at both system > and set level and adjust quota within range. i.e. > 1. IOMMU vendor driver(or other driver to use PASID w/o IOMMU) sets > system wide capacity during boot. > 2. VFIO Call ioasid_alloc_set() when allocating vfio_mm(), set default > quota > 3. Adjust quota per set with ioasid_adjust_set_size() as the tunable in > this patch. I think this is abstraction of the allocated PASID track logic in a common layer. It would simplify user logic. Regards, Yi Liu
