linux-kernel - Re: 2.6.22-rc6-mm1 Intel DMAR crash on AMD x86

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Date:	Fri, 29 Jun 2007 23:56:48 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>
Cc:	"Li, Shaohua" <shaohua.li@...el.com>,
	Robert Hancock <hancockr@...w.ca>, Zan Lynx <zlynx@....org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Raj, Ashok" <ashok.raj@...el.com>
Subject: Re: 2.6.22-rc6-mm1 Intel DMAR crash on AMD x86_64

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@...el.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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