Hi Bjorn,
On 11/16/21 4:38 AM, Bjorn Helgaas wrote:
On Mon, Nov 15, 2021 at 10:05:42AM +0800, Lu Baolu wrote:
From the perspective of who is initiating the device to do DMA, device
DMA could be divided into the following types:
DMA_OWNER_KERNEL: kernel device driver intiates the DMA
DMA_OWNER_USER: userspace device driver intiates the DMA
s/intiates/initiates/ (twice)
Yes.
As your first sentence suggests, the driver doesn't actually
*initiate* the DMA in either case. One of the drivers programs the
device, and the *device* initiates the DMA.
You are right. I could rephrase it as:
"From the perspective of who is controlling the device to do DMA ..."
DMA_OWNER_KERNEL and DMA_OWNER_USER are exclusive for all devices in
same iommu group as an iommu group is the smallest granularity of device
isolation and protection that the IOMMU subsystem can guarantee.
I think this basically says DMA_OWNER_KERNEL and DMA_OWNER_USER are
attributes of the iommu_group (not an individual device), and it
applies to all devices in the iommu_group. Below, you allude to the
fact that the interfaces are per-device. It's not clear to me why you
made a per-device interface instead of a per-group interface.
Yes, the attributes are of the iommu_group. We have both per-device and
per-iommu_group interfaces. The former is for device drivers and the
latter is only for vfio who has an iommu_group based iommu abstract.
This
extends the iommu core to enforce this exclusion when devices are
assigned to userspace.
Basically two new interfaces are provided:
int iommu_device_set_dma_owner(struct device *dev,
enum iommu_dma_owner mode, struct file *user_file);
void iommu_device_release_dma_owner(struct device *dev,
enum iommu_dma_owner mode);
Although above interfaces are per-device, DMA owner is tracked per group
under the hood. An iommu group cannot have both DMA_OWNER_KERNEL
and DMA_OWNER_USER set at the same time. Violation of this assumption
fails iommu_device_set_dma_owner().
Kernel driver which does DMA have DMA_OWNER_KENREL automatically
set/released in the driver binding process (see next patch).
s/DMA_OWNER_KENREL/DMA_OWNER_KERNEL/
Yes. Sorry for the typo.
Kernel driver which doesn't do DMA should not set the owner type (via a
new suppress flag in next patch). Device bound to such driver is considered
same as a driver-less device which is compatible to all owner types.
Userspace driver framework (e.g. vfio) should set DMA_OWNER_USER for
a device before the userspace is allowed to access it, plus a fd pointer to
mark the user identity so a single group cannot be operated by multiple
users simultaneously. Vice versa, the owner type should be released after
the user access permission is withdrawn.
Best regards,
baolu
