Hi,
Was exploring the implications of an application crash while DMA
is active from a vfio PCI device; the DMA being configured and
started by the application using vfio APIs.
The expectation is that, DMA is stopped/reset before we tear down the IOMMU mappings
and finally free the mmapped pages(on which DMA is happening).
>From the below stack trace(with dump_stack in vfio_pci_release),
[ 201.564273] [<ffffff8008798b50>] vfio_pci_release+0x80/0x458
[ 201.564276] [<ffffff8008792b74>] vfio_device_fops_release+0x2c/0x50
[ 201.564279] [<ffffff8008269ef4>] __fput+0x9c/0x218
[ 201.564283] [<ffffff800826a0e8>] ____fput+0x20/0x30
[ 201.564286] [<ffffff80080e7fe0>] task_work_run+0xa0/0xc8
[ 201.564289] [<ffffff80080cbc7c>] do_exit+0x2bc/0x9c8
[ 201.564293] [<ffffff80080cd0ec>] do_group_exit+0x3c/0xa8
[ 201.564296] [<ffffff80080d94c4>] get_signal+0x3e4/0x538
[ 201.564299] [<ffffff80080892f0>] do_signal+0x70/0x660
[ 201.564302] [<ffffff8008089ce8>] do_notify_resume+0xe0/0x120
PCI device is disabled/reset from vfio_pci_release invoked as part of
device fd release. The fd releases are in turn invoked from exit_files
and exit_task_work.
But exit_mm, gets called before exit_files/exit_task_work in do_exit.
Assuming all pages allocated/mmaped to a process gets freed in exit_mm,
is there is a possibility that user pages configured for DMA can get freed
to kernel before the vfio device is stopped/reset ?
Thanks.
--
Linu cherian
