RE: [PATCH v1 2/8] vfio/type1: Add vfio_iommu_type1 parameter for quota tuning

[Tian, Kevin]

> From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> Sent: Monday, March 30, 2020 4:53 PM
> 
> > From: Tian, Kevin <kevin.tian@xxxxxxxxx>
> > Sent: Monday, March 30, 2020 4:41 PM
> > To: Liu, Yi L <yi.l.liu@xxxxxxxxx>; alex.williamson@xxxxxxxxxx;
> > Subject: RE: [PATCH v1 2/8] vfio/type1: Add vfio_iommu_type1 parameter
> for quota
> > tuning
> >
> > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx>
> > > Sent: Sunday, March 22, 2020 8:32 PM
> > >
> > > From: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > >
> > > This patch adds a module option to make the PASID quota tunable by
> > > administrator.
> > >
> > > TODO: needs to think more on how to  make the tuning to be per-process.
> > >
> > > Previous discussions:
> > > https://patchwork.kernel.org/patch/11209429/
> > >
> > > Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> > > CC: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> > > Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>
> > > Cc: Eric Auger <eric.auger@xxxxxxxxxx>
> > > Cc: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > > Signed-off-by: Liu Yi L <yi.l.liu@xxxxxxxxx>
> > > ---
> > >  drivers/vfio/vfio.c             | 8 +++++++-
> > >  drivers/vfio/vfio_iommu_type1.c | 7 ++++++-
> > >  include/linux/vfio.h            | 3 ++-
> > >  3 files changed, 15 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c
> > > index d13b483..020a792 100644
> > > --- a/drivers/vfio/vfio.c
> > > +++ b/drivers/vfio/vfio.c
> > > @@ -2217,13 +2217,19 @@ struct vfio_mm
> *vfio_mm_get_from_task(struct
> > > task_struct *task)
> > >  }
> > >  EXPORT_SYMBOL_GPL(vfio_mm_get_from_task);
> > >
> > > -int vfio_mm_pasid_alloc(struct vfio_mm *vmm, int min, int max)
> > > +int vfio_mm_pasid_alloc(struct vfio_mm *vmm, int quota, int min, int
> max)
> > >  {
> > >  	ioasid_t pasid;
> > >  	int ret = -ENOSPC;
> > >
> > >  	mutex_lock(&vmm->pasid_lock);
> > >
> > > +	/* update quota as it is tunable by admin */
> > > +	if (vmm->pasid_quota != quota) {
> > > +		vmm->pasid_quota = quota;
> > > +		ioasid_adjust_set(vmm->ioasid_sid, quota);
> > > +	}
> > > +
> >
> > It's a bit weird to have quota adjusted in the alloc path, since the latter
> might
> > be initiated by non-privileged users. Why not doing the simple math in
> vfio_
> > create_mm to set the quota when the ioasid set is created? even in the
> future
> > you may allow per-process quota setting, that should come from separate
> > privileged path instead of thru alloc..
> 
> The reason is the kernel parameter modification has no event which
> can be used to adjust the quota. So I chose to adjust it in pasid_alloc
> path. If it's not good, how about adding one more IOCTL to let user-
> space trigger a quota adjustment event? Then even non-privileged
> user could trigger quota adjustment, the quota is actually controlled
> by privileged user. How about your opinion?
> 

why do you need an event to adjust? As I said, you can set the quota
when the set is created in vfio_create_mm...

Thanks
Kevin