Re: Re: [PATCH v4 2/5] iommu/vt-d: Remove the pasid present check in prq_event_thread

Joel Granados
2024-10-28T10:24:19Z

On Mon, Oct 28, 2024 at 03:50:46PM +0800, Yi Liu wrote:
> On 2024/10/16 05:08, Joel Granados wrote:
> > From: Klaus Jensen <k.jensen@samsung.com>
> >
> > PASID is not strictly needed when handling a PRQ event; remove the check
> > for the pasid present bit in the request. This change was not included
> > in the creation of prq.c to emphasize the change in capability checks
> > when handing PRQ events.
> >
> > Signed-off-by: Klaus Jensen <k.jensen@samsung.com>
> > Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> > Signed-off-by: Joel Granados <joel.granados@kernel.org>
>
> looks like the PRQ draining is missed for the PRI usage. When a pasid
> entry is destroyed, it might need to add helper similar to the
> intel_drain_pasid_prq() to drain PRQ for the non-pasid usage.

These types of user space PRIs (non-pasid, non-svm) are created by
making use of iommufd_hwpt_replace_device. Which adds an entry to the
pasid_array indexed on IOMMU_NO_PASID (0U) via the following path:

iommufd_hwpt_replace_device
-> iommufd_fault_domain_repalce_dev
-> __fault_domain_replace_dev
-> iommu_replace_group_handle
-> xa_reserve(&group->pasid_array, IOMMU_NO_PASID, GFP_KERNEL);

It is my understanding that this will provide the needed relation
between the device and the prq in such a way that when remove_dev_pasid
is called, intel_iommu_drain_pasid_prq will be called with the
appropriate pasid value set to IOMMU_NO_PASID. Please correct me if I'm
mistaken.

Does this answer your question? Do you have a specific path that you are
looking at where a specific non-pasid drain is needed?

Best

>
> > ---
> > drivers/iommu/intel/prq.c | 12 +++---------
> > 1 file changed, 3 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/iommu/intel/prq.c b/drivers/iommu/intel/prq.c
> > index d4f18eb46475..3c50c848893f 100644
> > --- a/drivers/iommu/intel/prq.c
> > +++ b/drivers/iommu/intel/prq.c
> > @@ -223,18 +223,12 @@ static irqreturn_t prq_event_thread(int irq, void *d)
> > req = &iommu->prq[head / sizeof(*req)];
> > address = (u64)req->addr << VTD_PAGE_SHIFT;
> >
> > - if (unlikely(!req->pasid_present)) {
> > - pr_err("IOMMU: %s: Page request without PASID\n",
> > - iommu->name);
> > -bad_req:
> > - handle_bad_prq_event(iommu, req, QI_RESP_INVALID);
> > - goto prq_advance;
> > - }
> > -
> > if (unlikely(!is_canonical_address(address))) {
> > pr_err("IOMMU: %s: Address is not canonical\n",
> > iommu->name);
> > - goto bad_req;
> > +bad_req:
> > + handle_bad_prq_event(iommu, req, QI_RESP_INVALID);
> > + goto prq_advance;
> > }
> >
> > if (unlikely(req->pm_req && (req->rd_req | req->wr_req))) {
> >
>
> --
> Regards,
> Yi Liu

--

Joel Granados