linux-kernel - Re: [PATCH] Disable Bus Master on PCI device shutdown

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Date:	Thu, 3 May 2012 17:52:10 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	linux-pci@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Disable Bus Master on PCI device shutdown

On Fri, Apr 27, 2012 at 1:00 PM, Khalid Aziz <khalid.aziz@...com> wrote:
> Disable Bus Master bit on the device in
> pci_device_shutdown() to ensure PCI devices do not continue
> to DMA data after shutdown. This can cause memory
> corruption in case of a kexec where the current kernel
> shuts down and transfers control to a new kernel while a
> PCI device continues to DMA to memory that does not belong
> to it any more in the new kernel.
>
> I have tested this code on two laptops, two workstations and
> a 16-socket server. kexec worked correctly on all of them.
>
>
> Signed-off-by: Khalid Aziz <khalid.aziz@...com>
> ---
>  drivers/pci/pci-driver.c |    6 ++++++
>  1 files changed, 6 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> index 6b54b23..9db5940 100644
> --- a/drivers/pci/pci-driver.c
> +++ b/drivers/pci/pci-driver.c
> @@ -420,6 +420,12 @@ static void pci_device_shutdown(struct device *dev)
>        pci_msi_shutdown(pci_dev);
>        pci_msix_shutdown(pci_dev);
>
> +       /*
> +        * Turn off Bus Master bit on the device to tell it to not
> +        * continue to do DMA
> +        */
> +       pci_disable_device(pci_dev);
> +
>        /*
>         * Devices may be enabled to wake up by runtime PM, but they need not
>         * be supposed to wake up the system from its "power off" state (e.g.

Any comment on this, Eric?  It seems reasonable to me.
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