Re: [PATCH v2] PCI: Explicitly put devices into D0 when initializing - Bug report

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 11 Jun 2025 06:50:59 -0700
Mario Limonciello <superm1@kernel.org> wrote:

> On 6/11/2025 5:52 AM, Cabiddu, Giovanni wrote:
> > Hi Mario, Bjorn and Alex,
> > 
> > On Wed, Apr 23, 2025 at 11:31:32PM -0500, Mario Limonciello wrote:  
> >> From: Mario Limonciello <mario.limonciello@amd.com>
> >>
> >> AMD BIOS team has root caused an issue that NVME storage failed to come
> >> back from suspend to a lack of a call to _REG when NVME device was probed.
> >>
> >> commit 112a7f9c8edbf ("PCI/ACPI: Call _REG when transitioning D-states")
> >> added support for calling _REG when transitioning D-states, but this only
> >> works if the device actually "transitions" D-states.
> >>
> >> commit 967577b062417 ("PCI/PM: Keep runtime PM enabled for unbound PCI
> >> devices") added support for runtime PM on PCI devices, but never actually
> >> 'explicitly' sets the device to D0.
> >>
> >> To make sure that devices are in D0 and that platform methods such as
> >> _REG are called, explicitly set all devices into D0 during initialization.
> >>
> >> Fixes: 967577b062417 ("PCI/PM: Keep runtime PM enabled for unbound PCI devices")
> >> Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
> >> ---  
> > Through a bisect, we identified that this patch, in v6.16-rc1,
> > introduces a regression on vfio-pci across all Intel QuickAssist (QAT)
> > devices. Specifically, the ioctl VFIO_GROUP_GET_DEVICE_FD call fails
> > with -EACCES.
> > 
> > Upon further investigation, the -EACCES appears to originate from the
> > rpm_resume() function, which is called by pm_runtime_resume_and_get()
> > within vfio_pci_core_enable(). Here is the exact call trace:
> > 
> >      drivers/base/power/runtime.c: rpm_resume()
> >      drivers/base/power/runtime.c: __pm_runtime_resume()
> >      include/linux/pm_runtime.h: pm_runtime_resume_and_get()
> >      drivers/vfio/pci/vfio_pci_core.c: vfio_pci_core_enable()
> >      drivers/vfio/pci/vfio_pci.c: vfio_pci_open_device()
> >      drivers/vfio/vfio_main.c: device->ops->open_device()
> >      drivers/vfio/vfio_main.c: vfio_df_device_first_open()
> >      drivers/vfio/vfio_main.c: vfio_df_open()
> >      drivers/vfio/group.c: vfio_df_group_open()
> >      drivers/vfio/group.c: vfio_device_open_file()
> >      drivers/vfio/group.c: vfio_group_ioctl_get_device_fd()
> >      drivers/vfio/group.c: vfio_group_fops_unl_ioctl(..., VFIO_GROUP_GET_DEVICE_FD, ...)
> > 
> > Is this a known issue that affects other devices? Is there any ongoing
> > discussion or fix in progress?
> > 
> > Thanks,
> >   
> 
> This is the first I've heard about an issue with that patch.
> 
> Does setting the VFIO parameter disable_idle_d3 help?
> 
> If so; this feels like an imbalance of runtime PM calls in the VFIO 
> stack that this patch exposed.
> 
> Alex, any ideas?

Does the device in question have a PM capability?  I note that
4d4c10f763d7 makes the sequence:

       pm_runtime_forbid(&dev->dev);
       pm_runtime_set_active(&dev->dev);
       pm_runtime_enable(&dev->dev);

Dependent on the presence of a PM capability.  The PM capability is
optional on SR-IOV VFs.  This feels like a bug in the original patch,
we should be able to use pm_runtime ops on a device without
specifically checking if the device supports PCI PM.

vfio-pci also has a somewhat unique sequence versus other drivers, we
don't call pci_enable_device() until the user opens the device, but we
want to put the device into low power before that occurs.  Historically
PCI-core left device in an unknown power state between driver uses, so
we've needed to manually move the device to D0 before calling
pm_runtime_allow() and pm_runtime_put() (see
vfio_pci_core_register_device()).  Possibly this is redundant now but
we're using pci_set_power_state() which shouldn't interact with
pm_runtime, so my initial guess is that we might be unbalanced because
this is a VF w/o a PM capability and we've missed the expected
pm_runtime initialization sequence.  Thanks,

Alex