Re: [PATCH] PCI: Enable Bus Master in pci_power_up()

[Lukas Wunner <lukas@wunner.de>]

On Tue, Jan 13, 2026 at 02:56:14PM -0600, Mario Limonciello (AMD) wrote:
> +++ b/drivers/pci/pci.c
> @@ -1323,6 +1323,7 @@ int pci_power_up(struct pci_dev *dev)
>  		return -EIO;
>  	}
>  
> +	pci_set_master(dev);
>  	pci_read_config_word(dev, dev->pm_cap + PCI_PM_CTRL, &pmcsr);
>  	if (PCI_POSSIBLE_ERROR(pmcsr)) {
>  		pci_err(dev, "Unable to change power state from %s to D0, device inaccessible\n",

So any device will be allowed to write to memory from the get-go?
That sounds like a very bad idea.  For security reasons alone,
we only want to enable bus mastering when needed.  It's up to
the driver to enable it, not up to the PCI core.  We've had cases
in the past where devices corrupted memory because BIOS left
bus mastering enabled, see abb2bafd295f.  Enabling bus mastering
for everything anytime will exacerbate such problems or uncover
new ones.

Thanks,

Lukas