Hi DeRossi,
On 2022/11/10 09:40, Anthony DeRossi wrote:
vfio_pci_dev_set_needs_reset() inspects the open_count of every device
in the set to determine whether a reset is allowed. The current device
always has open_count == 1 within vfio_pci_core_disable(), effectively
disabling the reset logic. This field is also documented as private in
vfio_device, so it should not be used to determine whether other devices
in the set are open.
haven't went through the prior version. maybe may question has been already
answered. My question is:
the major reason is the order problem in vfio_main.c. close_device() is
always called before decreasing open_count to be 0. So even other device
has no open fd, the current vfio_device still have one open count. So why
can't we just switch the order of open_count-- and close_device()?
Checking for vfio_device_set_open_count() > 1 on the device set fixes
both issues
tbh. it's weird to me that a driver needs to know the internal logic of
vfio core before knowing it needs to check the vfio_device_set_open_count()
in this way. Is vfio-pci the only driver that needs to do this check or
there are other drivers? If there are other drivers, maybe fixing the order
in core is better.
After commit 2cd8b14aaa66 ("vfio/pci: Move to the device set
infrastructure"), failure to create a new file for a device would cause
the reset to be skipped due to open_count being decremented after
calling close_device() in the error path.
After commit eadd86f835c6 ("vfio: Remove calls to
vfio_group_add_container_user()"), releasing a device would always skip
the reset due to an ordering change in vfio_device_fops_release().
Failing to reset the device leaves it in an unknown state, potentially
causing errors when it is accessed later or bound to a different driver.
This issue was observed with a Radeon RX Vega 56 [1002:687f] (rev c3)
assigned to a Windows guest. After shutting down the guest, unbinding
the device from vfio-pci, and binding the device to amdgpu:
[ 548.007102] [drm:psp_hw_start [amdgpu]] *ERROR* PSP create ring failed!
[ 548.027174] [drm:psp_hw_init [amdgpu]] *ERROR* PSP firmware loading failed
[ 548.027242] [drm:amdgpu_device_fw_loading [amdgpu]] *ERROR* hw_init of IP block <psp> failed -22
[ 548.027306] amdgpu 0000:0a:00.0: amdgpu: amdgpu_device_ip_init failed
[ 548.027308] amdgpu 0000:0a:00.0: amdgpu: Fatal error during GPU init
Fixes: 2cd8b14aaa66 ("vfio/pci: Move to the device set infrastructure")
Fixes: eadd86f835c6 ("vfio: Remove calls to vfio_group_add_container_user()")
Signed-off-by: Anthony DeRossi <ajderossi@xxxxxxxxx>
Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
drivers/vfio/pci/vfio_pci_core.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index badc9d828cac..e030c2120183 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -2488,12 +2488,12 @@ static bool vfio_pci_dev_set_needs_reset(struct vfio_device_set *dev_set)
struct vfio_pci_core_device *cur;
bool needs_reset = false;
- list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list) {
- /* No VFIO device in the set can have an open device FD */
- if (cur->vdev.open_count)
- return false;
+ /* No other VFIO device in the set can be open. */
+ if (vfio_device_set_open_count(dev_set) > 1)
+ return false;
+
+ list_for_each_entry(cur, &dev_set->device_list, vdev.dev_set_list)
needs_reset |= cur->needs_reset;
- }
return needs_reset;
}
--
Regards,
Yi Liu
