On 01/18/2013 06:42 AM, Konstantin Khlebnikov 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>
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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