On 11/28/21 4:02 PM, Greg Kroah-Hartman wrote:
On Sun, Nov 28, 2021 at 10:50:36AM +0800, Lu Baolu wrote:
The bus_type structure defines dma_configure() callback for bus drivers
to configure DMA on the devices. This adds the paired dma_unconfigure()
callback and calls it during driver unbinding so that bus drivers can do
some cleanup work.
One use case for this paired DMA callbacks is for the bus driver to check
for DMA ownership conflicts during driver binding, where multiple devices
belonging to a same IOMMU group (the minimum granularity of isolation and
protection) may be assigned to kernel drivers or user space respectively.
Without this change, for example, the vfio driver has to listen to a bus
BOUND_DRIVER event and then BUG_ON() in case of dma ownership conflict.
This leads to bad user experience since careless driver binding operation
may crash the system if the admin overlooks the group restriction. Aside
from bad design, this leads to a security problem as a root user, even with
lockdown=integrity, can force the kernel to BUG.
With this change, the bus driver could check and set the DMA ownership in
driver binding process and fail on ownership conflicts. The DMA ownership
should be released during driver unbinding.
Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Link: https://lore.kernel.org/linux-iommu/20210922123931.GI327412@xxxxxxxxxx/
Link: https://lore.kernel.org/linux-iommu/20210928115751.GK964074@xxxxxxxxxx/
Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
include/linux/device/bus.h | 3 +++
drivers/base/dd.c | 7 ++++++-
2 files changed, 9 insertions(+), 1 deletion(-)
diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h
index a039ab809753..ef54a71e5f8f 100644
--- a/include/linux/device/bus.h
+++ b/include/linux/device/bus.h
@@ -59,6 +59,8 @@ struct fwnode_handle;
* bus supports.
* @dma_configure: Called to setup DMA configuration on a device on
* this bus.
+ * @dma_unconfigure: Called to cleanup DMA configuration on a device on
+ * this bus.
"dma_cleanup()" is a better name for this, don't you think?
I agree with you. dma_cleanup() is more explicit and better here.
thanks,
greg k-h
Best regards,
baolu
