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

[Liu, Yi L]

> 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?

Regards,
Yi Liu