linux-kernel - RE: [PATCH v5 4/9] iommufd: Add fault and response message definitions

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Date: Wed, 15 May 2024 07:43:28 +0000
From: "Tian, Kevin" <kevin.tian@...el.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Jason Gunthorpe <jgg@...pe.ca>,
	"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>
CC: "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 4/9] iommufd: Add fault and response message
 definitions

> From: Lu Baolu <baolu.lu@...ux.intel.com>
> Sent: Tuesday, April 30, 2024 10:57 PM
> 
> iommu_hwpt_pgfaults represent fault messages that the userspace can
> retrieve. Multiple iommu_hwpt_pgfaults might be put in an iopf group,
> with the IOMMU_PGFAULT_FLAGS_LAST_PAGE flag set only for the last
> iommu_hwpt_pgfault.

Do you envision extending the same structure to report unrecoverable
fault in the future?

If yes this could be named more neutral e.g. iommu_hwpt_faults with
flags to indicate it's a recoverable PRI request.

If it's only for PRI probably iommu_hwpt_pgreqs is clearer.

> +
> +/**
> + * struct iommu_hwpt_pgfault - iommu page fault data
> + * @size: sizeof(struct iommu_hwpt_pgfault)
> + * @flags: Combination of enum iommu_hwpt_pgfault_flags
> + * @dev_id: id of the originated device
> + * @pasid: Process Address Space ID
> + * @grpid: Page Request Group Index
> + * @perm: Combination of enum iommu_hwpt_pgfault_perm
> + * @addr: Page address

'Fault address'

> + * @length: a hint of how much data the requestor is expecting to fetch. For
> + *          example, if the PRI initiator knows it is going to do a 10MB
> + *          transfer, it could fill in 10MB and the OS could pre-fault in
> + *          10MB of IOVA. It's default to 0 if there's no such hint.

This is not clear to me and I don't remember PCIe spec defines such
mechanism.

> +/**
> + * enum iommufd_page_response_code - Return status of fault handlers
> + * @IOMMUFD_PAGE_RESP_SUCCESS: Fault has been handled and the page
> tables
> + *                             populated, retry the access. This is the
> + *                             "Success" defined in PCI 10.4.2.1.
> + * @IOMMUFD_PAGE_RESP_INVALID: General error. Drop all subsequent
> faults
> + *                             from this device if possible. This is the
> + *                             "Response Failure" in PCI 10.4.2.1.
> + * @IOMMUFD_PAGE_RESP_FAILURE: Could not handle this fault, don't
> retry the
> + *                             access. This is the "Invalid Request" in PCI
> + *                             10.4.2.1.

the comment for 'INVALID' and 'FAILURE' are misplaced. Also I'd more
use the spec words to be accurate.

> + */
> +enum iommufd_page_response_code {
> +	IOMMUFD_PAGE_RESP_SUCCESS = 0,
> +	IOMMUFD_PAGE_RESP_INVALID,
> +	IOMMUFD_PAGE_RESP_FAILURE,
> +};
> +