linux-kernel - Re: [PATCH v6 05/10] iommufd: Add fault and response message definitions

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Message-ID: <20240612135219.GZ791043@ziepe.ca>
Date: Wed, 12 Jun 2024 10:52:19 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Lu Baolu <baolu.lu@...ux.intel.com>
Cc: 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 v6 05/10] iommufd: Add fault and response message
 definitions

On Mon, May 27, 2024 at 12:05:12PM +0800, Lu Baolu wrote:
> +/**
> + * 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: 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.
> + * @cookie: kernel-managed cookie identifying a group of fault messages. The
> + *          cookie number encoded in the last page fault of the group should
> + *          be echoed back in the response message.
> + */
> +struct iommu_hwpt_pgfault {
> +	__u32 size;

Given we fail the system call if size is not exactly the right value
we should probably drop it here.

The ioctl to get the FD can someday specify the format of the fault
messages if we need to upgrade. If we want to change it down the road
then the old FD will be exactly as it is now, and the user will
request a new format FD that only works in whatever the new way is.

Jason