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

On Thu, Apr 01, 2010 at 11:02:03AM -0400, Vivek Goyal wrote:
> On Thu, Apr 01, 2010 at 08:53:04AM -0400, Neil Horman wrote:
> > On Wed, Mar 31, 2010 at 10:24:18PM -0400, Vivek Goyal wrote:
> > > On Wed, Mar 31, 2010 at 09:13:11PM -0400, Neil Horman wrote:
> > > > On Wed, Mar 31, 2010 at 02:25:35PM -0700, Chris Wright wrote:
> > > > > * Neil Horman (nhorman@...) 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.
> > > > > 
> > > > Chris,
> > > > 	Can you elaborate on what you did with the iommu to make this safe?  It
> > > > will save me time digging through the history on this code, and help me
> > > > understand better whats going on here.
> > > > 
> > > > I was starting to think that we should just leave the iommu on through a kdump,
> > > > and re-construct a new page table based on the old table (filtered by the error