linux-kernel - Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

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Date: Mon, 20 May 2024 08:41:26 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>, "Liu, Yi L" <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joel Granados <j.granados@...sung.com>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "virtualization@...ts.linux-foundation.org"
 <virtualization@...ts.linux-foundation.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

On 5/15/24 3:57 PM, Tian, Kevin wrote:
>> From: Baolu Lu <baolu.lu@...ux.intel.com>
>> Sent: Wednesday, May 8, 2024 6:05 PM
>>
>> On 2024/5/8 8:11, Jason Gunthorpe wrote:
>>> On Tue, Apr 30, 2024 at 10:57:06PM +0800, Lu Baolu wrote:
>>>> diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
>>>> index ae65e0b85d69..1a0450a83bd0 100644
>>>> --- a/drivers/iommu/iommu-priv.h
>>>> +++ b/drivers/iommu/iommu-priv.h
>>>> @@ -36,6 +36,10 @@ struct iommu_attach_handle {
>>>>    			struct device	*dev;
>>>>    			refcount_t	users;
>>>>    		};
>>>> +		/* attach data for IOMMUFD */
>>>> +		struct {
>>>> +			void		*idev;
>>>> +		};
>>> We can use a proper type here, just forward declare it.
>>>
>>> But this sequence in the other patch:
>>>
>>> +       ret = iommu_attach_group(hwpt->domain, idev->igroup->group);
>>> +       if (ret) {
>>> +               iommufd_fault_iopf_disable(idev);
>>> +               return ret;
>>> +       }
>>> +
>>> +       handle = iommu_attach_handle_get(idev->igroup->group,
>> IOMMU_NO_PASID, 0);
>>> +       handle->idev = idev;
>>>
>>> Is why I was imagining the caller would allocate, because now we have
>>> the issue that a fault capable domain was installed into the IOMMU
>>> before it's handle could be fully setup, so we have a race where a
>>> fault could come in right between those things. Then what happens?
>>> I suppose we can retry the fault and by the time it comes back the
>>> race should resolve. A bit ugly I suppose.
>>
>> You are right. It makes more sense if the attached data is allocated and
>> managed by the caller. I will go in this direction and update my series.
>> I will also consider other review comments you have given in other
>> places.
>>
> 
> Does this direction imply a new iommu_attach_group_handle() helper
> to pass in the caller-allocated handle pointer or exposing a new
> iommu_group_set_handle() to set the handle to the group pasid_array
> and then having iomm_attach_group() to update the domain info in
> the handle?

I will add new iommu_attach/replace/detach_group_handle() helpers. Like
below:

+/**
+ * iommu_attach_group_handle - Attach an IOMMU domain to an IOMMU group
+ * @domain: IOMMU domain to attach
+ * @group: IOMMU group that will be attached
+ * @handle: attach handle
+ *
+ * Returns 0 on success and error code on failure.
+ *
+ * This is a variant of iommu_attach_group(). It allows the caller to 
provide
+ * an attach handle and use it when the domain is attached. This is 
currently
+ * only designed for IOMMUFD to deliver the I/O page faults.
+ */
+int iommu_attach_group_handle(struct iommu_domain *domain,
+                             struct iommu_group *group,
+                             struct iommu_attach_handle *handle)

Best regards,
baolu