linux-kernel - Re: [PATCH v5 5/9] iommufd: Add iommufd fault object

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Date: Fri, 24 May 2024 11:16:57 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: "Tian, Kevin" <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>,
	"Liu, Yi L" <yi.l.liu@...el.com>,
	Jacob Pan <jacob.jun.pan@...ux.intel.com>,
	Joel Granados <j.granados@...sung.com>,
	"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 5/9] iommufd: Add iommufd fault object

On Mon, May 20, 2024 at 09:24:09AM +0800, Baolu Lu wrote:
> On 5/15/24 4:37 PM, Tian, Kevin wrote:
> > > +static ssize_t iommufd_fault_fops_write(struct file *filep, const char __user
> > > *buf,
> > > +					size_t count, loff_t *ppos)
> > > +{
> > > +	size_t response_size = sizeof(struct iommu_hwpt_page_response);
> > > +	struct iommufd_fault *fault = filep->private_data;
> > > +	struct iommu_hwpt_page_response response;
> > > +	struct iommufd_device *idev = NULL;
> > > +	struct iopf_group *group;
> > > +	size_t done = 0;
> > > +	int rc;
> > > +
> > > +	if (*ppos || count % response_size)
> > > +		return -ESPIPE;
> > > +
> > > +	mutex_lock(&fault->mutex);
> > > +	while (count > done) {
> > > +		rc = copy_from_user(&response, buf + done, response_size);
> > > +		if (rc)
> > > +			break;
> > > +
> > > +		if (!idev || idev->obj.id != response.dev_id)
> > > +			idev = container_of(iommufd_get_object(fault->ictx,
> > > +							       response.dev_id,
> > > +
> > > IOMMUFD_OBJ_DEVICE),
> > > +					    struct iommufd_device, obj);
> > > +		if (IS_ERR(idev))
> > > +			break;
> > > +
> > > +		group = xa_erase(&idev->faults, response.cookie);
> > > +		if (!group)
> > > +			break;
> > is 'continue' better?
> 
> If we can't find a matched iopf group here, it means userspace provided
> something wrong. The current logic is that we stop here and tell
> userspace that only part of the faults have been responded to and it
> should retry the remaining responses with the right message.

The usual fd-ish error handling here should be to return a short write
(success) and then userspace will retry with the failing entry at the
start of the buffer and collect the errno.

Jason