linux-kernel - Re: [PATCH v4] PCI: Make sure the bus bridge powered on when scanning bus

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAJZ5v0hMxaVPsy9=w1nKhw1PbN0_8FnpJr5wPM24YZKy=--j9Q@mail.gmail.com>
Date:   Fri, 22 Apr 2022 13:31:56 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Yicong Yang <yangyicong@...ilicon.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Subject: Re: [PATCH v4] PCI: Make sure the bus bridge powered on when scanning bus

On Fri, Apr 22, 2022 at 10:06 AM Yicong Yang <yangyicong@...ilicon.com> wrote:
>
> When the bus bridge is runtime suspended, we'll fail to rescan
> the devices through sysfs as we cannot access the configuration
> space correctly when the bridge is in D3hot.
> It can be reproduced like:
>
> $ echo 1 > /sys/bus/pci/devices/0000:80:00.0/0000:81:00.1/remove
> $ echo 1 > /sys/bus/pci/devices/0000:80:00.0/pci_bus/0000:81/rescan
>
> 0000:80:00.0 is root port and is runtime suspended and we cannot
> get 0000:81:00.1 after rescan.

I would rephrase this in the following way:

0000:80:00.0 is a Root Port and it is runtime-suspended, so
0000:81:00.1 is unreachable after a rescan.

>
> Make bridge powered on when scanning the child bus, by adding

"Power up the bridge when scanning the child bus and allow it to
suspend again by adding ..."

> pm_runtime_get_sync()/pm_runtime_put() in pci_scan_child_bus_extend().
>
> Cc: Rafael J. Wysocki <rafael@...nel.org>
> Cc: Mika Westerberg <mika.westerberg@...ux.intel.com>
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>

With the above addressed, please feel free to add

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
> Change since v3:
> - retain the pm_runtime_*() calls in pci_scan_bridge_extend() as Rafael points
>   out that it's necessary when the brigde is in D3cold
> Link: https://lore.kernel.org/linux-pci/20220414123736.34150-1-yangyicong@hisilicon.com/
>
> Change since v2:
> - just rebase it on v5.18-rc2
> Link: https://lore.kernel.org/linux-pci/1601029386-4928-1-git-send-email-yangyicong@hisilicon.com/
>
> Change since v1:
> - use an intermediate variable *bridge as suggested
> - remove the pm_runtime_*() calls in pci_scan_bridge_extend()
> Link: https://lore.kernel.org/linux-pci/1596022223-4765-1-git-send-email-yangyicong@hisilicon.com/
>
>  drivers/pci/probe.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 17a969942d37..b108e72b6586 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -2859,11 +2859,20 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
>         unsigned int used_buses, normal_bridges = 0, hotplug_bridges = 0;
>         unsigned int start = bus->busn_res.start;
>         unsigned int devfn, fn, cmax, max = start;
> +       struct pci_dev *bridge = bus->self;
>         struct pci_dev *dev;
>         int nr_devs;
>
>         dev_dbg(&bus->dev, "scanning bus\n");
>
> +       /*
> +        * Make sure the bus bridge is powered on, otherwise we may not be
> +        * able to scan the devices as we may fail to access the configuration
> +        * space of subordinates.
> +        */
> +       if (bridge)
> +               pm_runtime_get_sync(&bridge->dev);
> +
>         /* Go find them, Rover! */
>         for (devfn = 0; devfn < 256; devfn += 8) {
>                 nr_devs = pci_scan_slot(bus, devfn);
> @@ -2976,6 +2985,9 @@ static unsigned int pci_scan_child_bus_extend(struct pci_bus *bus,
>                 }
>         }
>
> +       if (bridge)
> +               pm_runtime_put(&bridge->dev);
> +
>         /*
>          * We've scanned the bus and so we know all about what's on
>          * the other side of any bridges that may be on this bus plus
> --
> 2.24.0
>