linux-kernel - Re: [PATCH] nvme-pci: Shutdown the device if D3Cold is allowed by the user

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

Message-ID: <20241209144314.ow2qgrhiwr23qw6g@thinkpad>
Date: Mon, 9 Dec 2024 20:13:14 +0530
From: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: kbusch@...nel.org, axboe@...nel.dk, hch@....de, sagi@...mberg.me,
	linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, andersson@...nel.org,
	konradybcio@...nel.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH] nvme-pci: Shutdown the device if D3Cold is allowed by
 the user

On Thu, Dec 05, 2024 at 07:49:34PM -0600, Bjorn Helgaas wrote:
> On Thu, Dec 05, 2024 at 05:29:00PM -0600, Bjorn Helgaas wrote:
> > On Sat, Nov 23, 2024 at 02:31:13PM +0530, Manivannan Sadhasivam wrote:
> > > On Fri, Nov 22, 2024 at 04:20:50PM -0600, Bjorn Helgaas wrote:
> > > > On Mon, Nov 18, 2024 at 01:53:44PM +0530, Manivannan Sadhasivam wrote:
> > > > > PCI core allows users to configure the D3Cold state for each PCI
> > > > > device through the sysfs attribute
> > > > > '/sys/bus/pci/devices/.../d3cold_allowed'. This attribute sets
> > > > > the 'pci_dev:d3cold_allowed' flag and could be used by users to
> > > > > allow/disallow the PCI devices to enter D3Cold during system
> > > > > suspend.
> > ...
> 
> > > We did attempt to solve this problem in multiple ways, but the
> > > lesson learned was, kernel cannot decide the power mode without help
> > > from userspace. That's the reason I wanted to make use of this
> > > 'd3cold_allowed' sysfs attribute to allow userspace to override the
> > > D3Cold if it wants based on platform requirement.
> > 
> > It seems sub-optimal that this only works how you want if the user
> > intervenes.
> 
> Oops, I think I got this part backwards.  The patch uses PCI PM if
> d3cold_allowed is set, and it's set by default, so it does what you
> need for the Qualcomm platform *without* user intervention.
> 
> But I guess using the flag allows users in other situations to force
> use of NVMe power management by clearing d3cold_allowed via sysfs.
> Does that mean some unspecified other platforms might only work
> correctly with that user intervention?

The 'unspecified platforms' would be Android devices making use of NVMe, which
is not a reality now but a possibility in the future. But even when it happens,
it won't be a problem for Android as it has userspace knobs to control the power
state of the storage devices (as like how it controls UFS power states today).

UFS Reference:

'/sys/bus/platform/devices/*.ufs/spm_lvl' documented in:
Documentation/ABI/testing/sysfs-driver-ufs

- Mani

-- 
மணிவண்ணன் சதாசிவம்