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PCI/sysfs: Protect driver's D3cold preference from user space

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struct pci_dev contains two flags which govern whether the device may
suspend to D3cold:

* no_d3cold provides an opt-out for drivers (e.g. if a device is known
  to not wake from D3cold)

* d3cold_allowed provides an opt-out for user space (default is true,
  user space may set to false)

Since commit 9d26d3a8f1 ("PCI: Put PCIe ports into D3 during suspend"),
the user space setting overwrites the driver setting.  Essentially user
space is trusted to know better than the driver whether D3cold is
working.

That feels unsafe and wrong.  Assume that the change was introduced
inadvertently and do not overwrite no_d3cold when d3cold_allowed is
modified.  Instead, consider d3cold_allowed in addition to no_d3cold
when choosing a suspend state for the device.

That way, user space may opt out of D3cold if the driver hasn't, but it
may no longer force an opt in if the driver has opted out.

Fixes: 9d26d3a8f1 ("PCI: Put PCIe ports into D3 during suspend")
Link: https://lore.kernel.org/r/b8a7f4af2b73f6b506ad8ddee59d747cbf834606.1695025365.git.lukas@wunner.de
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Cc: stable@vger.kernel.org	# v4.8+
This commit is contained in:
Lukas Wunner 2023-09-18 14:48:01 +02:00 committed by Bjorn Helgaas
parent 0bb80ecc33
commit 70b70a4307
2 changed files with 2 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
drivers/pci/pci-acpi.c
View File

@ -911,7 +911,7 @@ pci_power_t acpi_pci_choose_state(struct pci_dev *pdev)
{
int acpi_state, d_max;
if (pdev->no_d3cold)
if (pdev->no_d3cold || !pdev->d3cold_allowed)
d_max = ACPI_STATE_D3_HOT;
else
d_max = ACPI_STATE_D3_COLD;

5
drivers/pci/pci-sysfs.c
View File

@ -530,10 +530,7 @@ static ssize_t d3cold_allowed_store(struct device *dev,
return -EINVAL;
pdev->d3cold_allowed = !!val;
if (pdev->d3cold_allowed)
pci_d3cold_enable(pdev);
else
pci_d3cold_disable(pdev);
pci_bridge_d3_update(pdev);
pm_runtime_resume(dev);