Re: [PATCH 4/5] PCI: don't touch enable_cnt in pci_device_shutdown()

[Bjorn Helgaas]

[+cc Khalid new email addr]

On Mon, Jan 28, 2013 at 4:40 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Fri, Jan 18, 2013 at 4:42 AM, Konstantin Khlebnikov
> <khlebnikov@xxxxxxxxxx> wrote:
>> comment in commit b566a22c23327f18ce941ffad0ca907e50a53d41
>> ("PCI: disable Bus Master on PCI device shutdown") says:
>>
>> | 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.
>>
>> Seems like pci_clear_master() must be used here instead of pci_disable_device(),
>> because it disables Bus Muster unconditionally and doesn't changes enable_cnt.
>>
>> Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx>
>> Cc: linux-pci@xxxxxxxxxxxxxxx
>> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
>> Cc: Khalid Aziz <khalid.aziz@xxxxxx>
>> ---
>>  drivers/pci/pci-driver.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
>> index 030dbf0..853d605 100644
>> --- a/drivers/pci/pci-driver.c
>> +++ b/drivers/pci/pci-driver.c
>> @@ -392,7 +392,7 @@ static void pci_device_shutdown(struct device *dev)
>>          * Turn off Bus Master bit on the device to tell it to not
>>          * continue to do DMA
>>          */
>> -       pci_disable_device(pci_dev);
>> +       pci_clear_master(pci_dev);
>
> We currently only call pci_enable_device() and pci_disable_device()
> from drivers, and I think that's a nice division that's worth keeping.
>  It keeps the core's mitts off device operation and helps preserve the
> enable_cnt integrity.  So I like this change from that perspective.
>
> Any objections to this, Khalid?
>
>>  }
>>
>>  #ifdef CONFIG_PM
>>
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