This topic came up before when Khalid posted a similar patch -
https://lkml.org/lkml/2012/6/6/278. I don't know that consensus was ever
reached but the thread does present a lot of opinions and experiences in
this area so probably worth reading/noting.
Myron
On Fri, Jan 18, 2013 at 9:16 AM, Don Dutile <ddut...@redhat.com> wrote:
> On 01/18/2013 06:42 AM, Konstantin Khlebnikov wrote:
>
>> comment in commit b566a22c23327f18ce941ffad0ca90**7e50a53d41
>> ("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@openvz.**org<khlebni...@openvz.org>
>> >
>> Cc: linux-...@vger.kernel.org
>> Cc: Bjorn Helgaas<bhelg...@google.com>
>> Cc: Khalid Aziz<khalid.a...@hp.com>
>>
>
> Hmmm.... wondering if this was the problem why kexec folks
> said that device_shutdown() didn't work on all systems (when
> trying to stop DMA, esp. on IOMMU-enabled systems...).
>
> Bjorn: do you have a list &/or contact in kexec space to try this
> patch vs the "reset every PCI bus" strategy that is currently
> being pushed for kexec's method to halt DMA from a PCI device ?
>
> ---
>> 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);
>> }
>>
>> #ifdef CONFIG_PM
>>
>> --
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>
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