linux-kernel - Re: [PATCH v2] PCI: Explicitly put devices into D0 when initializing

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Message-ID: <aEmrJSqhApz/sRe8@gcabiddu-mobl.ger.corp.intel.com>
Date: Wed, 11 Jun 2025 17:13:25 +0100
From: "Cabiddu, Giovanni" <giovanni.cabiddu@...el.com>
To: Alex Williamson <alex.williamson@...hat.com>
CC: Mario Limonciello <superm1@...nel.org>, <bhelgaas@...gle.com>,
	<mario.limonciello@....com>, <rafael.j.wysocki@...el.com>,
	<huang.ying.caritas@...il.com>, <stern@...land.harvard.edu>,
	<linux-pci@...r.kernel.org>, <mike.ximing.chen@...el.com>,
	<ahsan.atta@...el.com>, <suman.kumar.chakraborty@...el.com>,
	<kvm@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] PCI: Explicitly put devices into D0 when initializing
 - Bug report

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@...nel.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@....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@....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,

-- 
Giovanni