Re: [PATCH] PCI/VPD: Add runtime power management to sysfs interface

[Eric Auger]

Hi Alex,

On 7/7/23 17:10, Alex Williamson wrote:
> Unlike default access to config space through sysfs, the vpd read and
> write function don't actively manage the runtime power management state
> of the device during access.  Since commit 7ab5e10eda02 ("vfio/pci: Move
> the unused device into low power state with runtime PM"), the vfio-pci
> driver will use runtime power management and release unused devices to
> make use of low power states.  Attempting to access VPD information in
> this low power state can result in incorrect information or kernel
> crashes depending on the system behavior.
>
> Wrap the vpd read/write bin attribute handlers in runtime PM and take
> into account the potential quirk to select the correct device to wake.

This much improved the situation as it is more difficult to hit the
issue. Unfortunately after tens of attempts I was still able to hit a
kernel crash. The console output does not mention the VPD anymore but
PCI power management events (PME).



[  168.616700] CPU: 0 PID: 1409 Comm: kworker/0:5 Not tainted
6.4.0-vpd-upstream+ #56
[  168.624257] Hardware name: GIGABYTE R181-T90-00/MT91-FS1-00, BIOS F34
08/13/2020
[  168.631639] Workqueue: events_freezable pci_pme_list_scan
[  168.637032] pstate: 604000c9 (nZCv daIF +PAN -UAO -TCO -DIT -SSBS
BTYPE=--)
[  168.643982] pc : pci_generic_config_read+0x64/0xd8
[  168.648763] lr : pci_generic_config_read+0x28/0xd8
[  168.653542] sp : ffff80008caebcb0
[  168.656844] x29: ffff80008caebcb0 x28: 0000000000000000 x27:
0000000000000000
[  168.663969] x26: 0000000000000000 x25: 0000000000000000 x24:
ffff80008caebd76
[  168.671094] x23: ffff0008063fd800 x22: 0000000000000044 x21:
ffff80008232d4c8
[  168.678218] x20: ffff80008caebd24 x19: 0000000000000002 x18:
00000000000040fc
[  168.685342] x17: 00000000000040f8 x16: 0000000000000000 x15:
0000000000000001
[  168.692466] x14: ffffffffffffffff x13: 0000000000000000 x12:
0101010101010101
[  168.699590] x11: 7f7f7f7f7f7f7f7f x10: fefefefefefefeff x9 :
ffff8000807b3938
[  168.706714] x8 : fefefefefefefeff x7 : 0000000000000018 x6 :
000000000000007f
[  168.713838] x5 : 0000000000000000 x4 : ffff800090000000 x3 :
0000000000000000
[  168.720962] x2 : 0000000000000044 x1 : 0000000000c00044 x0 :
ffff800090c00044
[  168.728086] Call trace:
[  168.730520]  pci_generic_config_read+0x64/0xd8
[  168.734953]  pci_bus_read_config_word+0x84/0xe8
[  168.739471]  pci_read_config_word+0x30/0x50
[  168.743642]  pci_check_pme_status+0x70/0xa8
[  168.747813]  pci_pme_list_scan+0x84/0x158
[  168.751811]  process_one_work+0x1ec/0x488
[  168.755810]  worker_thread+0x48/0x400
[  168.759461]  kthread+0x10c/0x120
[  168.762678]  ret_from_fork+0x10/0x20
[  168.766245] Code: 52800000 a94153f3 a8c27bfd d65f03c0 (79400000)
[  168.772326] ---[ end trace 0000000000000000 ]---
[  168.776931] Kernel panic - not syncing: synchronous external abort:
Fatal exception
[  168.784574] SMP: stopping secondary CPUs
[  169.831001] SMP: failed to stop secondary CPUs 0,199
[  169.835955] Kernel Offset: 0x190000 from 0xffff800080000000


Thanks

Eric
>
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
>  drivers/pci/vpd.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/vpd.c b/drivers/pci/vpd.c
> index a4fc4d0690fe..81217dd4789f 100644
> --- a/drivers/pci/vpd.c
> +++ b/drivers/pci/vpd.c
> @@ -275,8 +275,23 @@ static ssize_t vpd_read(struct file *filp, struct kobject *kobj,
>  			size_t count)
>  {
>  	struct pci_dev *dev = to_pci_dev(kobj_to_dev(kobj));
> +	struct pci_dev *vpd_dev = dev;
> +	ssize_t ret;
> +
> +	if (dev->dev_flags & PCI_DEV_FLAGS_VPD_REF_F0) {
> +		vpd_dev = pci_get_func0_dev(dev);
> +		if (!vpd_dev)
> +			return -ENODEV;
> +	}
> +
> +	pci_config_pm_runtime_get(vpd_dev);
> +	ret = pci_read_vpd(vpd_dev, off, count, buf);
> +	pci_config_pm_runtime_put(vpd_dev);
> +
> +	if (dev != vpd_dev)
> +		pci_dev_put(vpd_dev);
>  
> -	return pci_read_vpd(dev, off, count, buf);
> +	return ret;
>  }
>  
>  static ssize_t vpd_write(struct file *filp, struct kobject *kobj,
> @@ -284,8 +299,23 @@ static ssize_t vpd_write(struct file *filp, struct kobject *kobj,
>  			 size_t count)
>  {
>  	struct pci_dev *dev = to_pci_dev(kobj_to_dev(kobj));
> +	struct pci_dev *vpd_dev = dev;
> +	ssize_t ret;
> +
> +	if (dev->dev_flags & PCI_DEV_FLAGS_VPD_REF_F0) {
> +		vpd_dev = pci_get_func0_dev(dev);
> +		if (!vpd_dev)
> +			return -ENODEV;
> +	}
> +
> +	pci_config_pm_runtime_get(vpd_dev);
> +	ret = pci_write_vpd(vpd_dev, off, count, buf);
> +	pci_config_pm_runtime_put(vpd_dev);
> +
> +	if (dev != vpd_dev)
> +		pci_dev_put(vpd_dev);
>  
> -	return pci_write_vpd(dev, off, count, buf);
> +	return ret;
>  }
>  static BIN_ATTR(vpd, 0600, vpd_read, vpd_write, 0);
>