linux-kernel - Re: [PATCH] PCI: Make d3cold_allowed sysfs attribute read only

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Date:   Tue, 3 Oct 2023 11:30:54 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     bhelgaas@...gle.com, lukas@...ner.de, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI: Make d3cold_allowed sysfs attribute read only

On 10/3/2023 04:44, Mika Westerberg wrote:
> On Mon, Oct 02, 2023 at 01:10:25PM -0500, Mario Limonciello wrote:
>> Before d3cold was stable userspace was allowed to influence the kernel's
>> decision of whether to enable d3cold for a device by a sysfs file
>> `d3cold_allowed`.  This potentially allows userspace to break the suspend
>> for the system.
>>
>> For debugging purposes `pci_port_pm=` can be used to control whether
>> a PCI port will go into D3cold and runtime PM can be turned off by
>> sysfs on PCI end points.
>>
>> Change the sysfs attribute to read-only and simplify the internal kernel
>> logic to avoid needing to store the userspace request.
> 
> I wonder if this ends up breaking some userspace apps? Not objecting
> though, just wanted to mention ;-)
> 
> One thing we could do is to taint the kernel or log a warning if
> userspace touches this but allow it to do so.

If we collectively decide it needs to stay RW for userspace compatbility 
then I'll respin it to keep the store call but ignore whatever is 
written, return -EINVAL and emit a pr_warn_once() that it's a no-op.