[PATCH] amd iommu: force flush of iommu prior during shutdown

[Chris Wright]

* Neil Horman (nhorman at tuxdriver.com) wrote:
> Flush iommu during shutdown
> 
> When using an iommu, its possible, if a kdump kernel boot follows a primary
> kernel crash, that dma operations might still be in flight from the previous
> kernel during the kdump kernel boot.  This can lead to memory corruption,
> crashes, and other erroneous behavior, specifically I've seen it manifest during
> a kdump boot as endless iommu error log entries of the form:
> AMD-Vi: Event logged [IO_PAGE_FAULT device=00:14.1 domain=0x000d
> address=0x000000000245a0c0 flags=0x0070]

We've already fixed this problem once before, so some code shift must
have brought it back.  Personally, I prefer to do this on the bringup
path than the teardown path.  Besides keeping the teardown path as
simple as possible (goal is to get to kdump kernel asap), there's also
reason to competely flush on startup in genernal in case BIOS has done
anything unsavory.

thanks,
-chris