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

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Message-ID: <ujexsgcpvcjux2ugfes6mzjxl53j3icarfbu25imhzliqskyv6@l7f42nv4fhmy>
Date: Mon, 28 Oct 2024 11:24:14 +0100
From: Joel Granados <joel.granados@...nel.org>
To: Yi Liu <yi.l.liu@...el.com>
Cc: David Woodhouse <dwmw2@...radead.org>, 
	Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
	Robin Murphy <robin.murphy@....com>, Jason Gunthorpe <jgg@...pe.ca>, 
	Kevin Tian <kevin.tian@...el.com>, Klaus Jensen <its@...elevant.dk>, linux-kernel@...r.kernel.org, 
	iommu@...ts.linux.dev, Klaus Jensen <k.jensen@...sung.com>
Subject: Re: Re: [PATCH v4 2/5] iommu/vt-d: Remove the pasid present check in
 prq_event_thread

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@...sung.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@...sung.com>
> > Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> > Signed-off-by: Joel Granados <joel.granados@...nel.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