Re: [RFC PATCH 0/1] iommu: Detach device from domain when removed from group

Gerald Schaefer
2015-08-03T12:25:48Z

On Tue, 28 Jul 2015 19:55:55 +0200
Gerald Schaefer <gerald.schaefer@de.ibm.com> wrote:

> Hi,
>
> during IOMMU API function testing on s390 I hit the following scenario:
>
> After binding a device to vfio-pci, the user completes the VFIO_SET_IOMMU
> ioctl and stops, see the sample C program below. Now the device is manually
> removed via "echo 1 > /sys/bus/pci/devices/.../remove".
>
> Although the SET_IOMMU ioctl triggered the attach_dev callback in the
> underlying IOMMU API, removing the device in this way won't trigger the
> detach_dev callback, neither during remove nor when the user program
> continues with closing group/container.
>
> On s390, this eventually leads to a kernel panic when binding the device
> again to its non-vfio PCI driver, because of the missing arch-specific
> cleanup in detach_dev. On x86, the detach_dev callback will also not be
> called directly, but there is a notifier that will catch
> BUS_NOTIFY_REMOVED_DEVICE and eventually do the cleanup. Other
> architectures w/o the notifier probably have at least some kind of memory
> leak in this scenario, so a general fix would be nice.
>
> My first approach was to try and fix this in VFIO code, but Alex Williamson
> pointed me to some asymmetry in the IOMMU code: iommu_group_add_device()
> will invoke the attach_dev callback, but iommu_group_remove_device() won't
> trigger detach_dev. Fixing this asymmetry would fix the issue for me, but
> is this the correct fix? Any thoughts?

Ping.

The suggested fix may be completely wrong, but not having detach_dev called
seems like like a serious issue, any feedback would be greatly appreciated.

>
> Regards,
> Gerald
>
>
> Here is the sample C program to trigger the ioctl:
>
> #include <stdio.h>
> #include <fcntl.h>
> #include <linux/vfio.h>
>
> int main(void)
> {
> int container, group, rc;
>
> container = open("/dev/vfio/vfio", O_RDWR);
> if (container < 0) {
> perror("open /dev/vfio/vfio\n");
> return -1;
> }
>
> group = open("/dev/vfio/0", O_RDWR);
> if (group < 0) {
> perror("open /dev/vfio/0\n");
> return -1;
> }
>
> rc = ioctl(group, VFIO_GROUP_SET_CONTAINER, &container);
> if (rc) {
> perror("ioctl VFIO_GROUP_SET_CONTAINER\n");
> return -1;
> }
>
> rc = ioctl(container, VFIO_SET_IOMMU, VFIO_TYPE1_IOMMU);
> if (rc) {
> perror("ioctl VFIO_SET_IOMMU\n");
> return -1;
> }
>
> printf("Try device remove...\n");
> getchar();
>
> close(group);
> close(container);
> return 0;
> }
>
> Gerald Schaefer (1):
> iommu: Detach device from domain when removed from group
>
> drivers/iommu/iommu.c | 5 +++++
> 1 file changed, 5 insertions(+)
>