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

Jason Gunthorpe
2024-05-08T00:11:23Z

On Tue, Apr 30, 2024 at 10:57:06PM +0800, Lu Baolu wrote:
> diff --git a/drivers/iommu/iommu-priv.h b/drivers/iommu/iommu-priv.h
> index ae65e0b85d69..1a0450a83bd0 100644
> --- a/drivers/iommu/iommu-priv.h
> +++ b/drivers/iommu/iommu-priv.h
> @@ -36,6 +36,10 @@ struct iommu_attach_handle {
> struct device *dev;
> refcount_t users;
> };
> + /* attach data for IOMMUFD */
> + struct {
> + void *idev;
> + };

We can use a proper type here, just forward declare it.

But this sequence in the other patch:

+ ret = iommu_attach_group(hwpt->domain, idev->igroup->group);
+ if (ret) {
+ iommufd_fault_iopf_disable(idev);
+ return ret;
+ }
+
+ handle = iommu_attach_handle_get(idev->igroup->group, IOMMU_NO_PASID, 0);
+ handle->idev = idev;

Is why I was imagining the caller would allocate, because now we have
the issue that a fault capable domain was installed into the IOMMU
before it's handle could be fully setup, so we have a race where a
fault could come in right between those things. Then what happens?
I suppose we can retry the fault and by the time it comes back the
race should resolve. A bit ugly I suppose.

> diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
> index 83b45dce94a4..1819b28e9e6b 100644
> --- a/include/uapi/linux/iommufd.h
> +++ b/include/uapi/linux/iommufd.h
> @@ -50,6 +50,7 @@ enum {
> IOMMUFD_CMD_HWPT_SET_DIRTY_TRACKING,
> IOMMUFD_CMD_HWPT_GET_DIRTY_BITMAP,
> IOMMUFD_CMD_HWPT_INVALIDATE,
> + IOMMUFD_CMD_FAULT_ALLOC,
> };

I think I'd call this a CMD_FAULT_QUEUE_ALLOC - does that make sense?

Jason