linux-kernel - Re: [PATCH v5 3/9] iommu: Add attachment handle to struct iopf

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Date: Fri, 10 May 2024 22:30:10 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, Kevin Tian <kevin.tian@...el.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>, Yi Liu <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Joel Granados <j.granados@...sung.com>, iommu@...ts.linux.dev,
 virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 3/9] iommu: Add attachment handle to struct iopf_group

On 2024/5/10 21:38, Jason Gunthorpe wrote:
> On Fri, May 10, 2024 at 11:14:20AM +0800, Baolu Lu wrote:
>> On 5/8/24 8:04 AM, Jason Gunthorpe wrote:
>>> On Tue, Apr 30, 2024 at 10:57:04PM +0800, Lu Baolu wrote:
>>>> @@ -206,8 +197,11 @@ void iommu_report_device_fault(struct device *dev, struct iopf_fault *evt)
>>>>    	if (group == &abort_group)
>>>>    		goto err_abort;
>>>> -	group->domain = get_domain_for_iopf(dev, fault);
>>>> -	if (!group->domain)
>>>> +	if (!(fault->prm.flags & IOMMU_FAULT_PAGE_REQUEST_PASID_VALID) ||
>>>> +	    get_attach_handle_for_iopf(dev, fault->prm.pasid, group))
>>>> +		get_attach_handle_for_iopf(dev, IOMMU_NO_PASID, group);
>>> That seems a bit weird looking?
>> Agreed.
>>
>>> get_attach_handle_for_iopf(dev,
>>>      (fault->prm.flags &
>>>      IOMMU_FAULT_PAGE_REQUEST_PASID_VALID) ? fault->prm.pasid : IOMMU_NO_PASID,
>>>      group);
>> The logic here is that it tries the PASID domain and if it doesn't
>> exist, then tries the RID domain as well. I explained this in the commit
>> message:
>>
>> "
>> ... if the pasid table of a device is wholly managed by user space,
>> there is no domain attached to the PASID of the device ...
>> "
> Okay, it needs a comment in the code, and the RID fallback should be
> based aroudn checking for a NESTING domain type which includes the
> PASID table. (ie ARM and AMD not Intel)
It appears that Intel is just special. ARM, AMD, and RISC-V all support
a NESTING domain which includes the PASID table. So, how about defining
a special NESTING domain type for Intel? Like this,

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 35ae9a6f73d3..09b4e671dcee 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -173,6 +173,8 @@ struct iommu_domain_geometry {

  #define __IOMMU_DOMAIN_NESTED  (1U << 6)  /* User-managed address 
space nested
                                               on a stage-2 translation 
       */
+#define __IOMMU_DOMAIN_PASID   (1U << 7)  /* User-managed domain for a
+                                             specific PASID*/

  #define IOMMU_DOMAIN_ALLOC_FLAGS ~__IOMMU_DOMAIN_DMA_FQ
  /*
@@ -204,6 +206,9 @@ struct iommu_domain_geometry {
  #define IOMMU_DOMAIN_SVA       (__IOMMU_DOMAIN_SVA)
  #define IOMMU_DOMAIN_PLATFORM  (__IOMMU_DOMAIN_PLATFORM)
  #define IOMMU_DOMAIN_NESTED    (__IOMMU_DOMAIN_NESTED)
+#define IOMMU_DOMAIN_NESTED_PASID                              \
+                               (__IOMMU_DOMAIN_NESTED |        \
+                                __IOMMU_DOMAIN_PASID)

And current IOMMU_DOMAIN_NESTED domain type is just for a nesting domain
with PASID table.

The Intel IOMMU driver will convert to use IOMMU_DOMAIN_NESTED_PASID in
the PASID interface series.

> We shouldn't just elevate a random PASID to the RID if it isn't
> approprite..

If above propose looks good to you, then I just need to add a domain
type check before RID fallback.

Best regards,
baolu