linux-kernel - Re: [PATCH v5 7/9] iommufd: Associate fault object with iommufd_hw

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Date: Fri, 10 May 2024 11:23:49 +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 7/9] iommufd: Associate fault object with
 iommufd_hw_pgtable

On 5/8/24 8:25 AM, Jason Gunthorpe wrote:
> On Tue, Apr 30, 2024 at 10:57:08PM +0800, Lu Baolu wrote:
>>   /**
>> @@ -412,6 +415,9 @@ enum iommu_hwpt_data_type {
>>    * @data_type: One of enum iommu_hwpt_data_type
>>    * @data_len: Length of the type specific data
>>    * @data_uptr: User pointer to the type specific data
>> + * @fault_id: The ID of IOMMUFD_FAULT object. Valid only if flags field of
>> + *            IOMMU_HWPT_FAULT_ID_VALID is set.
>> + * @__reserved2: Padding to 64-bit alignment. Must be 0.
>>    *
>>    * Explicitly allocate a hardware page table object. This is the same object
>>    * type that is returned by iommufd_device_attach() and represents the
>> @@ -442,6 +448,8 @@ struct iommu_hwpt_alloc {
>>   	__u32 data_type;
>>   	__u32 data_len;
>>   	__aligned_u64 data_uptr;
>> +	__u32 fault_id;
>> +	__u32 __reserved2;
>>   };
>>   #define IOMMU_HWPT_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_HWPT_ALLOC)
> [..]
> 
>> @@ -359,7 +359,7 @@ static const struct iommufd_ioctl_op iommufd_ioctl_ops[] = {
>>   	IOCTL_OP(IOMMU_GET_HW_INFO, iommufd_get_hw_info, struct iommu_hw_info,
>>   		 __reserved),
>>   	IOCTL_OP(IOMMU_HWPT_ALLOC, iommufd_hwpt_alloc, struct iommu_hwpt_alloc,
>> -		 __reserved),
>> +		 __reserved2),
> This is now how the back compat mechanism works. The value here is the
> absolute minimum size, it should never increase. The first __reserved
> is always the right value.
> 
> If you change it then old userspace that doesn't include the fault_id
> will stop working.

Yeah! I will remove this change.

Best regards,
baolu