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

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Date:   Tue, 28 Jun 2022 19:02:25 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.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:     baolu.lu@...ux.intel.com, 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

On 2022/6/28 16:39, Tian, Kevin wrote:
>>   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.

I had some comments around iommu_queue_iopf() in the previous patch. The
iommu_queue_iopf() is the generic page fault handler exposed by iommu
core, hence that's the right place to document this.

Post it below as well:

diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
index 1df8c1dcae77..aee9e033012f 100644
--- a/drivers/iommu/io-pgfault.c
+++ b/drivers/iommu/io-pgfault.c
@@ -181,6 +181,13 @@ static void iopf_handle_group(struct work_struct *work)
   * request completes, outstanding faults will have been dealt with by 
the time
   * the PASID is freed.
   *
+ * Any valid page fault will be eventually routed to an iommu domain 
and the
+ * page fault handler installed there will get called. The users of this
+ * handling framework should guarantee that the iommu domain could only be
+ * freed after the device has stopped generating page faults (or the iommu
+ * hardware has been set to block the page faults) and the pending page 
faults
+ * have been flushed.
+ *
   * Return: 0 on success and <0 on error.
   */
  int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)

Best regards,
baolu