linux-kernel - Re: [PATCH v3 5/8] iommufd: Associate fault object with iommufd_hw

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Date: Mon, 25 Mar 2024 12:59:46 +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 v3 5/8] iommufd: Associate fault object with
 iommufd_hw_pgtable

On 2024/3/23 1:06, Jason Gunthorpe wrote:
> On Fri, Mar 15, 2024 at 09:16:43AM +0800, Baolu Lu wrote:
>> On 3/9/24 3:05 AM, Jason Gunthorpe wrote:
>>> On Mon, Jan 22, 2024 at 03:39:00PM +0800, Lu Baolu wrote:
>>>
>>>> @@ -411,6 +414,8 @@ enum iommu_hwpt_data_type {
>>>>     * @__reserved: Must be 0
>>>>     * @data_type: One of enum iommu_hwpt_data_type
>>>>     * @data_len: Length of 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.
>>>>     * @data_uptr: User pointer to the type specific data
>>>>     *
>>>>     * Explicitly allocate a hardware page table object. This is the same object
>>>> @@ -441,6 +446,7 @@ struct iommu_hwpt_alloc {
>>>>    	__u32 __reserved;
>>>>    	__u32 data_type;
>>>>    	__u32 data_len;
>>>> +	__u32 fault_id;
>>>>    	__aligned_u64 data_uptr;
>>>>    };
>>>
>>> ?? We can't add fault_id in the middle of the struct??
>>
>> Yes. I should add the new field at the end.
>>
>> By the way, with a __u32 added, this data structure is not 64-byte-
>> aligned anymore. Do we need to add another unused u32 entry, or just let
>> the compiler handle it?
> 
> Yes, add a reserved u32 to ensure the structs is always without
> implicit padding.

Sure.

> 
>>>
>>>> +	if (cmd->flags & IOMMU_HWPT_FAULT_ID_VALID) {
>>>> +		struct iommufd_fault *fault;
>>>> +
>>>> +		fault = iommufd_get_fault(ucmd, cmd->fault_id);
>>>> +		if (IS_ERR(fault)) {
>>>> +			rc = PTR_ERR(fault);
>>>> +			goto out_hwpt;
>>>> +		}
>>>> +		hwpt->fault = fault;
>>>> +		hwpt->domain->iopf_handler = iommufd_fault_iopf_handler;
>>>> +		hwpt->domain->fault_data = hwpt;
>>>> +		hwpt->fault_capable = true;
>>>
>>> I wonder if there should be an iommu API to make a domain fault
>>> capable?
>>
>> The iommu core identifies a fault-capable domain by checking its
>> domain->iopf_handler. Anyway, what's the difference between a fault or
>> non-fault capable domain from iommu core's point of view?
> 
>  From the core? Nothing. I'm just wondering from an API perspective if
> we should have a little inline to indicate it.

I have no objection if there's a consumer for it.

Best regards,
baolu