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

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Date: Wed, 8 May 2024 18:05:06 +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 5/9] iommufd: Add iommufd fault object

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.

Best regards,
baolu