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

Liu, Yi L
2020-03-30T08:53:04Z

> From: Tian, Kevin <kevin.tian@intel.com>
> Sent: Monday, March 30, 2020 4:41 PM
> To: Liu, Yi L <yi.l.liu@intel.com>; alex.williamson@redhat.com;
> Subject: RE: [PATCH v1 2/8] vfio/type1: Add vfio_iommu_type1 parameter for quota
> tuning
>
> > From: Liu, Yi L <yi.l.liu@intel.com>
> > Sent: Sunday, March 22, 2020 8:32 PM
> >
> > From: Liu Yi L <yi.l.liu@intel.com>
> >
> > 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@intel.com>
> > CC: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Cc: Alex Williamson <alex.williamson@redhat.com>
> > Cc: Eric Auger <eric.auger@redhat.com>
> > Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>
> > Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
> > ---
> > 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