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

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Message-ID: <20100401024421.GA5877@redhat.com>
Date:	Wed, 31 Mar 2010 22:44:21 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Neil Horman <nhorman@...driver.com>,
	iommu@...ts.linux-foundation.org, joerg.roedel@....com,
	hbabu@...ibm.com, kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amd iommu: force flush of iommu prior during shutdown

On Wed, Mar 31, 2010 at 02:25:35PM -0700, Chris Wright wrote:
> * Neil Horman (nhorman@...driver.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.

Can we flush domains (all the I/O TLBs assciated with each domain), during
initialization? I think all the domain data built by previous kernel will
be lost and new kernel will have no idea about. 

Thanks
Vivek
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