Date: Thu, 1 Apr 2010 00:10:40 -0700
From: Chris Wright <chrisw@sous-sol.org>
Subject: Re: [PATCH] amd iommu: force flush of iommu prior during shutdown
Message-ID: <20100401071040.GU29241@sequoia.sous-sol.org>
References: <20100331152417.GB13406@hmsreliant.think-freely.org>
	<20100331212535.GR29241@sequoia.sous-sol.org>
	<20100401024421.GA5877@redhat.com>
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To: Vivek Goyal <vgoyal@redhat.com>
Cc: Neil Horman <nhorman@tuxdriver.com>, joerg.roedel@amd.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Chris Wright <chrisw@sous-sol.org>, hbabu@us.ibm.com, iommu@lists.linux-foundation.org

* Vivek Goyal (vgoyal@redhat.com) wrote:
> On Wed, Mar 31, 2010 at 02:25:35PM -0700, Chris Wright wrote:
> > * Neil Horman (nhorman@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.
> 
> 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. 

We first invalidate the device table entry, so new translation requests
will see the new domainid for a given BDF.  Then we invalidate the
whole set of page tables associated w/ the new domainid.  Now all dma
transactions will need page table walk (page tables will be empty excpet
for any 1:1 mappings).  Any old domainid's from previous kernel that
aren't found in new device table entries are effectively moot.  Just so
happens that in kexec/kdump case, they'll be the same domainid's, but
that doesn't matter.

thanks,
-chris

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