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Message-ID: <abc94be4-a909-4255-bb08-f0fcf45a21b8@linux.intel.com>
Date: Fri, 8 Dec 2023 19:43:12 +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>,
iommu@...ts.linux.dev, linux-kselftest@...r.kernel.org,
virtualization@...ts.linux-foundation.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/6] iommufd: Deliver fault messages to user space
On 2023/12/1 23:24, Jason Gunthorpe wrote:
> On Thu, Oct 26, 2023 at 10:49:28AM +0800, Lu Baolu wrote:
>
>> +static ssize_t hwpt_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 hw_pgtable_fault *fault = filep->private_data;
>> + struct iommu_hwpt_page_response response;
>> + struct iommufd_hw_pagetable *hwpt;
>> + struct iopf_group *iter, *group;
>> + struct iommufd_device *idev;
>> + size_t done = 0;
>> + int rc = 0;
>> +
>> + if (*ppos || count % response_size)
>> + return -ESPIPE;
>> +
>> + mutex_lock(&fault->mutex);
>> + while (!list_empty(&fault->response) && count > done) {
>> + rc = copy_from_user(&response, buf + done, response_size);
>> + if (rc)
>> + break;
>> +
>> + /* Get the device that this response targets at. */
>> + idev = container_of(iommufd_get_object(fault->ictx,
>> + response.dev_id,
>> + IOMMUFD_OBJ_DEVICE),
>> + struct iommufd_device, obj);
>> + if (IS_ERR(idev)) {
>> + rc = PTR_ERR(idev);
>> + break;
>> + }
>
> See here it might be better to have a per-fd list of outstanding
> faults per-fd and then the cookie would just index that list, then you
> get everything in one shot instead of having to do a xarray looking
> and then a linear list search
Yours is more efficient. I will do it that way in the next version.
>
>> +static const struct file_operations hwpt_fault_fops = {
>> + .owner = THIS_MODULE,
>> + .read = hwpt_fault_fops_read,
>> + .write = hwpt_fault_fops_write,
>> +};
>
> nonseekable_open() behavior should be integrated into this
Sure.
>
>> +static int hw_pagetable_get_fault_fd(struct hw_pgtable_fault *fault)
>> +{
>> + struct file *filep;
>> + int fdno;
>> +
>> + fdno = get_unused_fd_flags(O_CLOEXEC);
>> + if (fdno < 0)
>> + return fdno;
>> +
>> + filep = anon_inode_getfile("[iommufd-pgfault]", &hwpt_fault_fops,
>> + fault, O_RDWR);
>> + if (IS_ERR(filep)) {
>> + put_unused_fd(fdno);
>> + return PTR_ERR(filep);
>> + }
>> +
>> + fd_install(fdno, filep);
>> + fault->fault_file = filep;
>> + fault->fault_fd = fdno;
>
> fd_install must be the very last thing before returning success from a
> system call because we cannot undo it.
Yes.
>
> There are other failure paths before here and the final return
>
> Jason
Best regards,
baolu
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