linux-kernel - RE: [PATCH v9 10/11] iommu: Per-domain I/O page fault handling

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Date:   Tue, 28 Jun 2022 08:39:36 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>, Vinod Koul <vkoul@...nel.org>
CC:     Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.org>
Subject: RE: [PATCH v9 10/11] iommu: Per-domain I/O page fault handling

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, June 21, 2022 10:44 PM
> 
> Tweak the I/O page fault handling framework to route the page faults to
> the domain and call the page fault handler retrieved from the domain.
> This makes the I/O page fault handling framework possible to serve more
> usage scenarios as long as they have an IOMMU domain and install a page
> fault handler in it. Some unused functions are also removed to avoid
> dead code.
> 
> The iommu_get_domain_for_dev_pasid() which retrieves attached domain
> for a {device, PASID} pair is used. It will be used by the page fault
> handling framework which knows {device, PASID} reported from the iommu
> driver. We have a guarantee that the SVA domain doesn't go away during
> IOPF handling, because unbind() waits for pending faults with
> iopf_queue_flush_dev() before freeing the domain. Hence, there's no need
> to synchronize life cycle of the iommu domains between the unbind() and
> the interrupt threads.

I found iopf_queue_flush_dev() is only called in intel-iommu driver. Did
I overlook anything?

>  static void iopf_handle_group(struct work_struct *work)
>  {
>  	struct iopf_group *group;
> +	struct iommu_domain *domain;
>  	struct iopf_fault *iopf, *next;
>  	enum iommu_page_response_code status =
> IOMMU_PAGE_RESP_SUCCESS;
> 
>  	group = container_of(work, struct iopf_group, work);
> +	domain = iommu_get_domain_for_dev_pasid(group->dev,
> +				group->last_fault.fault.prm.pasid);
> +	if (!domain || !domain->iopf_handler)
> +		status = IOMMU_PAGE_RESP_INVALID;

Miss a comment on why no refcnt is required on domain as explained
in the commit msg.