linux-kernel - Re: [PATCH v3 3/8] iommufd: Add fault and response message definitions

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Date: Thu, 14 Mar 2024 21:41:45 +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 3/8] iommufd: Add fault and response message
 definitions

On 2024/3/9 1:50, Jason Gunthorpe wrote:
> On Mon, Jan 22, 2024 at 03:38:58PM +0800, Lu Baolu wrote:
> 
>> +/**
>> + * enum iommu_hwpt_pgfault_flags - flags for struct iommu_hwpt_pgfault
>> + * @IOMMU_PGFAULT_FLAGS_PASID_VALID: The pasid field of the fault data is
>> + *                                   valid.
>> + * @IOMMU_PGFAULT_FLAGS_LAST_PAGE: It's the last fault of a fault group.
>> + */
>> +enum iommu_hwpt_pgfault_flags {
>> +	IOMMU_PGFAULT_FLAGS_PASID_VALID		= (1 << 0),
>> +	IOMMU_PGFAULT_FLAGS_LAST_PAGE		= (1 << 1),
>> +};
>> +
>> +/**
>> + * enum iommu_hwpt_pgfault_perm - perm bits for struct iommu_hwpt_pgfault
>> + * @IOMMU_PGFAULT_PERM_READ: request for read permission
>> + * @IOMMU_PGFAULT_PERM_WRITE: request for write permission
>> + * @IOMMU_PGFAULT_PERM_EXEC: request for execute permission
>> + * @IOMMU_PGFAULT_PERM_PRIV: request for privileged permission
> 
> You are going to have to elaborate what PRIV is for.. We don't have
> any concept of this in the UAPI for iommufd so what is a userspace
> supposed to do if it hits this? EXEC is similar, we can't actually
> enable exec permissions from userspace IIRC..

The PCIe spec, section "10.4.1 Page Request Message" and "6.20.2 PASID
Information Layout":

The PCI PASID TLP Prefix defines "Execute Requested" and "Privileged
Mode Requested" bits.

PERM_EXEC indicates a page request with a PASID that has the "Execute
Requested" bit set. Similarly, PERM_PRIV indicates a page request with a
  PASID that has "Privileged Mode Requested" bit set.

> 
>> +enum iommu_hwpt_pgfault_perm {
>> +	IOMMU_PGFAULT_PERM_READ			= (1 << 0),
>> +	IOMMU_PGFAULT_PERM_WRITE		= (1 << 1),
>> +	IOMMU_PGFAULT_PERM_EXEC			= (1 << 2),
>> +	IOMMU_PGFAULT_PERM_PRIV			= (1 << 3),
>> +};
>> +
>> +/**
>> + * 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
>> + */
>> +struct iommu_hwpt_pgfault {
>> +	__u32 size;
>> +	__u32 flags;
>> +	__u32 dev_id;
>> +	__u32 pasid;
>> +	__u32 grpid;
>> +	__u32 perm;
>> +	__u64 addr;
>> +};
> 
> Do we need an addr + size here? I've seen a few things where I wonder
> if that might become an enhancment someday.

I am not sure. The page size is not part of ATS/PRI. Can you please
elaborate a bit about how the size could be used? Perhaps I
misunderstood here?

> 
>> +/**
>> + * struct iommu_hwpt_page_response - IOMMU page fault response
>> + * @size: sizeof(struct iommu_hwpt_page_response)
>> + * @flags: Must be set to 0
>> + * @dev_id: device ID of target device for the response
>> + * @pasid: Process Address Space ID
>> + * @grpid: Page Request Group Index
>> + * @code: response code. The supported codes include:
>> + *        0: Successful; 1: Response Failure; 2: Invalid Request.
> 
> This should be an enum

Sure.

> 
>> + * @addr: The fault address. Must match the addr field of the
>> + *        last iommu_hwpt_pgfault of a reported iopf group.
>> + */
>> +struct iommu_hwpt_page_response {
>> +	__u32 size;
>> +	__u32 flags;
>> +	__u32 dev_id;
>> +	__u32 pasid;
>> +	__u32 grpid;
>> +	__u32 code;
>> +	__u64 addr;
>> +};
> 
> Do we want some kind of opaque ID value from the kernel here to match
> request with response exactly? Or is the plan to search on the addr?

I am using the "addr" as the opaque data to search request in this
series. Is it enough?

Best regards,
baolu