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Message-ID: <20240612132358.GU791043@ziepe.ca>
Date: Wed, 12 Jun 2024 10:23:58 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Lu Baolu <baolu.lu@...ux.intel.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 v6 06/10] iommufd: Add iommufd fault object
On Fri, Jun 07, 2024 at 09:17:28AM +0000, Tian, Kevin wrote:
> > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > Sent: Monday, May 27, 2024 12:05 PM
> >
> > +static ssize_t iommufd_fault_fops_read(struct file *filep, char __user *buf,
> > + size_t count, loff_t *ppos)
> > +{
> > + size_t fault_size = sizeof(struct iommu_hwpt_pgfault);
> > + struct iommufd_fault *fault = filep->private_data;
> > + struct iommu_hwpt_pgfault data;
> > + struct iommufd_device *idev;
> > + struct iopf_group *group;
> > + struct iopf_fault *iopf;
> > + size_t done = 0;
> > + int rc = 0;
> > +
> > + if (*ppos || count % fault_size)
> > + return -ESPIPE;
>
> the man page says:
>
> "If count is zero, read() returns zero and has no other results."
The above does that? 0 % X == 0
> > +
> > + mutex_lock(&fault->mutex);
> > + while (!list_empty(&fault->deliver) && count > done) {
> > + group = list_first_entry(&fault->deliver,
> > + struct iopf_group, node);
> > +
> > + if (group->fault_count * fault_size > count - done)
> > + break;
> > +
> > + rc = xa_alloc(&fault->response, &group->cookie, group,
> > + xa_limit_32b, GFP_KERNEL);
> > + if (rc)
> > + break;
> > +
> > + idev = to_iommufd_handle(group->attach_handle)->idev;
> > + list_for_each_entry(iopf, &group->faults, list) {
> > + iommufd_compose_fault_message(&iopf->fault,
> > + &data, idev,
> > + group->cookie);
> > + rc = copy_to_user(buf + done, &data, fault_size);
> > + if (rc) {
>
> 'rc' should be converted to -EFAULT.
Yes
> > + xa_erase(&fault->response, group->cookie);
> > + break;
> > + }
> > + done += fault_size;
> > + }
> > +
> > + list_del(&group->node);
> > + }
> > + mutex_unlock(&fault->mutex);
> > +
> > + return done == 0 ? rc : done;
>
> again this doesn't match the manual:
>
> "On error, -1 is returned, and errno is set appropriately. "
>
> it doesn't matter whether 'done' is 0.
It is setup so that once the list_del() below happens it is guarenteed
that the system call will return a positive result so that the
list_del'd items are always returned to userspace.
If we hit any fault here on the Nth item we should still return the
prior items and ignore the fault.
If we hit a fault on the first item then we should return the fault.
Jason
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