linux-kernel - Re: [PATCH v7 07/10] iommufd: Fault-capable hwpt attach/detach/replace

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Date: Mon, 1 Jul 2024 13:55:12 +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 v7 07/10] iommufd: Fault-capable hwpt
 attach/detach/replace

On 2024/6/29 5:17, Jason Gunthorpe wrote:
> On Sun, Jun 16, 2024 at 02:11:52PM +0800, Lu Baolu wrote:
>> +static int iommufd_fault_iopf_enable(struct iommufd_device *idev)
>> +{
>> +	struct device *dev = idev->dev;
>> +	int ret;
>> +
>> +	/*
>> +	 * Once we turn on PCI/PRI support for VF, the response failure code
>> +	 * should not be forwarded to the hardware due to PRI being a shared
>> +	 * resource between PF and VFs. There is no coordination for this
>> +	 * shared capability. This waits for a vPRI reset to recover.
>> +	 */
>> +	if (dev_is_pci(dev) && to_pci_dev(dev)->is_virtfn)
>> +		return -EINVAL;
> I don't quite get this remark, isn't not supporting PRI on VFs kind of
> useless? What is the story here?

This remark is trying to explain why attaching an iopf-capable hwpt to a
VF is not supported for now. The PCI sepc (section 10.4.2.1) states that
a response failure will disable the PRI on the function. But for PF/VF
case, the PRI is a shared resource, therefore a response failure on a VF
might cause iopf on other VFs to malfunction. So, we start from simple
by not allowing it.

Best regards,
baolu