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

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Date:   Tue, 3 Oct 2023 12:44:07 +0300
From:   Mika Westerberg <mika.westerberg@...ux.intel.com>
To:     Mario Limonciello <mario.limonciello@....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 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.