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

[Giovanni Cabiddu <giovanni.cabiddu@intel.com>]

On Wed, Jun 11, 2025 at 01:45:49PM -0700, Mario Limonciello wrote:
> On 6/11/2025 9:13 AM, Cabiddu, Giovanni wrote:
> > On Wed, Jun 11, 2025 at 10:00:02AM -0600, Alex Williamson wrote:
> > > 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,
> > 
> > Yes, for Intel QAT, the issue occurs with a VF without the PM capability.
> > 
> > Thanks,
> > 
> 
> Got it, thanks Alex!  I think this should help return it to previous
> behavior for devices without runtime PM and still fix the problem it needed
> to.
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 3dd44d1ad829..c495c3c692f5 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -3221,15 +3221,17 @@ void pci_pm_init(struct pci_dev *dev)
> 
>         /* find PCI PM capability in list */
>         pm = pci_find_capability(dev, PCI_CAP_ID_PM);
> -       if (!pm)
> +       if (!pm) {
> +               goto poweron;
>                 return;
> +       }
>         /* Check device's ability to generate PME# */
>         pci_read_config_word(dev, pm + PCI_PM_PMC, &pmc);
> 
>         if ((pmc & PCI_PM_CAP_VER_MASK) > 3) {
>                 pci_err(dev, "unsupported PM cap regs version (%u)\n",
>                         pmc & PCI_PM_CAP_VER_MASK);
> -               return;
> +               goto poweron;
>         }
> 
>         dev->pm_cap = pm;
> @@ -3274,6 +3276,7 @@ void pci_pm_init(struct pci_dev *dev)
>         pci_read_config_word(dev, PCI_STATUS, &status);
>         if (status & PCI_STATUS_IMM_READY)
>                 dev->imm_ready = 1;
> +poweron:
>         pci_pm_power_up_and_verify_state(dev);
>         pm_runtime_forbid(&dev->dev);
>         pm_runtime_set_active(&dev->dev);

I tried this change and it works.

Thanks,

-- 
Giovanni