linux-kernel - Re: [PATCH v2 0/2] PCI: Protect VPD and PME accesses from power management

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Date:   Thu, 10 Aug 2023 12:54:18 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, eric.auger@...hat.com
Subject: Re: [PATCH v2 0/2] PCI: Protect VPD and PME accesses from power
 management

On Thu, 10 Aug 2023 13:29:44 -0500
Bjorn Helgaas <helgaas@...nel.org> wrote:

> On Thu, Aug 03, 2023 at 11:12:31AM -0600, Alex Williamson wrote:
> > Since v5.19, vfio-pci makes use of runtime power management on devices.
> > This has the effect of potentially putting entire sub-hierarchies into
> > lower power states, which has exposed some gaps in the PCI subsystem
> > around power management support.
> > 
> > The first issue is that lspci accesses the VPD sysfs interface, which
> > does not provide the same power management wrappers as general config
> > space.
> > 
> > The next covers PME, where we attempt to skip devices based on their PCI
> > power state, but don't protect changes to that state or look at the
> > overall runtime power management state of the device.
> > 
> > This latter patch addresses the issue noted by Eric in the follow-ups to
> > v1 linked below.
> > 
> > These patches are logically independent, but only together resolve an
> > issue on Eric's system where a pair of endpoints bound to vfio-pci and
> > unused by userspace drivers trigger faults through lspci and PME
> > polling.  Thanks,
> > 
> > Alex 
> > 
> > v1: https://lore.kernel.org/all/20230707151044.1311544-1-alex.williamson@redhat.com/
> > 
> > Alex Williamson (2):
> >   PCI/VPD: Add runtime power management to sysfs interface
> >   PCI: Fix runtime PM race with PME polling
> > 
> >  drivers/pci/pci.c | 23 ++++++++++++++++-------
> >  drivers/pci/vpd.c | 34 ++++++++++++++++++++++++++++++++--
> >  2 files changed, 48 insertions(+), 9 deletions(-)  
> 
> Applied with the tweak below to pci/vpd for v6.6, thanks!  The idea is
> to match the pci_get_func0_dev() so the get/put balance is clear
> without having to analyze PCI_DEV_FLAGS_VPD_REF_F0 usage:
> 
> -       if (dev != vpd_dev)
> +       if (dev->dev_flags & PCI_DEV_FLAGS_VPD_REF_F0)
> 

Looks good, thanks!

Alex