On Mon, 30 Mar 2020 11:44:08 +0000 "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > > From: Liu, Yi L <yi.l.liu@xxxxxxxxx> > > Sent: Monday, March 30, 2020 5:27 PM > > > > > From: Tian, Kevin <kevin.tian@xxxxxxxxx> > > > Sent: Monday, March 30, 2020 5:20 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: 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... > > > > oh, it's to support runtime adjustments. I guess it may be helpful to let > > per-VM quota tunable even the VM is running. If just set the quota in > > vfio_create_mm(), it is not able to adjust at runtime. > > > > ok, I didn't note the module parameter was granted with a write permission. > However there is a further problem. We cannot support PASID reclaim now. > What about the admin sets a quota smaller than previous value while some > IOASID sets already exceed the new quota? I'm not sure how to fail a runtime > module parameter change due to that situation. possibly a normal sysfs > node better suites the runtime change requirement... Yep, making this runtime adjustable seems a bit unpredictable and racy, and it's not clear to me how a user is going to jump in at just the right time for a user and adjust the limit. I'd probably go for a simple non-runtime adjustable module option. It's a safety net at this point anyway afaict. Thanks, Alex
