From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: "Keshavamurthy, Anil S" <anil.s.keshavamurthy@intel.com>
Subject: Re: 2.6.22-rc6-mm1 Intel DMAR crash on AMD x86_64
Date: Fri, 29 Jun 2007 23:56:48 +0200
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Cc: "Li, Shaohua" <shaohua.li@intel.com>, Robert Hancock <hancockr@shaw.ca>,
       Zan Lynx <zlynx@acm.org>, Andrew Morton <akpm@linux-foundation.org>,
       linux-kernel@vger.kernel.org, "Raj, Ashok" <ashok.raj@intel.com>
References: <46845943.7050005@shaw.ca> <FC1D1B23302A22499C60C967336B2AE0016F7529@pdsmsx411.ccr.corp.intel.com> <20070629152858.GA27995@linux-os.sc.intel.com>
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On Friday, 29 June 2007 17:28, Keshavamurthy, Anil S wrote:
> On Thu, Jun 28, 2007 at 06:14:27PM -0700, Li, Shaohua wrote:
> > 
> > 
> > ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.22-
> > >rc6/2.6.22-rc6-mm1/
> > >>
> > >>> +intel-iommu-dmar-detection-and-parsing-logic.patch
> [..]
> > >
> > >I took a picture of it, looks like the backtrace is:
> > >
> > >NULL pointer dereference at 024
> > >EIP:dmar_table_init+0x11
> > >intel_iommu_init+0x30
> > >pci_iommu_init+0xe
> > >kernel_init+0x16e
> > >
> > >Presumably something is NULL in dmar_table_init that wasn't expected to
> > >be.. I would guess it likely crashes on any system without an Intel
> > >IOMMU in it.
> Yup, that is correct.
> 
> > How about something like below?
> > 
> > 
> > int __init dmar_table_init(void)
> > {
> > +	if (!dmar_tbl)
> > +		return -ENODEV;
> > 	parse_dmar_table();
> why not check for NULL in the function where it touched?
> Also when there are no DMAR devices we need the below
> printk on the console.
> 
> > 	if (list_empty(&dmar_drhd_units)) {
> > 		printk(KERN_ERR PREFIX "No DMAR devices found\n");
> > 		return -ENODEV;
> > 	}
> > 	return 0;
> > }
> 
> Here is the revised patch of the above.
> Andrew, please add this fix to
> +intel-iommu-dmar-detection-and-parsing-logic.patch
> ------------------------------------------------
> 
> Check for dmar_tbl pointer as this can be NULL on 
> systems with no Intel VT-d support.
> 
> Signed-off-by: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>

For the record, this patch fixes the boot crash on my AMD64-based test box.

Thanks,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
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