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Date:	Thu, 10 Apr 2014 11:36:51 -0400
From:	Linda Knippers <linda.knippers@...com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Woodhouse, David" <david.woodhouse@...el.com>
CC:	"bhe@...hat.com" <bhe@...hat.com>,
	"linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"James.Bottomley@...senpartnership.com" 
	<James.Bottomley@...senpartnership.com>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	"davidlohr@...com" <davidlohr@...com>,
	"scameron@...rdog.cce.hp.com" <scameron@...rdog.cce.hp.com>,
	"jiang.liu@...ux.intel.com" <jiang.liu@...ux.intel.com>
Subject: Re: hpsa driver bug crack kernel down!

On 4/10/2014 11:14 AM, Bjorn Helgaas wrote:
> On Thu, Apr 10, 2014 at 2:46 AM, Woodhouse, David
> <david.woodhouse@...el.com> wrote:
> 
>>>>>>>>>>> DMAR:[fault reason 02] Present bit in context entry is clear
>>>>>>>>>>> dmar: DRHD: handling fault status reg 602
>>>>>>>>>>> dmar: DMAR:[DMA Read] Request device [02:00.0] fault addr 7f61e000
>>
>> That "Present bit in context entry is clear" fault means that we have
>> not set up *any* mappings for this PCI device… on this IOMMU.
>>
>>>> Yes, specifically (finally done bisecting):
>>>>
>>>> commit 2e45528930388658603ea24d49cf52867b928d3e
>>>> Author: Jiang Liu <jiang.liu@...ux.intel.com>
>>>> Date:   Wed Feb 19 14:07:36 2014 +0800
>>>>
>>>>     iommu/vt-d: Unify the way to process DMAR device scope array
>>
>> This commit is about how we decide which IOMMU a given PCI device is
>> attached to.
>>
>> Thus, my first guess would be that we are quite happily setting up the
>> requested DMA maps on the *wrong* IOMMU, and then taking faults when the
>> device actually tries to do DMA.
>>
>> However, I'm not 100% convinced of that. The fault address looks
>> suspiciously like a true physical address, not a virtual bus address of
>> the type that we'd normally allocate for a dma_map_* operation. Those
>> would start at 0xfffff000 and work downwards, typically.
> 
> I like the "wrong IOMMU (or no IOMMU at all)" theory.  If we didn't
> connect the device with an IOMMU at all, that would explain the device
> DMAing directly to a physical address, wouldn't it?
> 
>> Do you have 'iommu=pt' on the kernel command line? Can I see the full
>> dmesg as this system boots, and also a copy of the DMAR table?

This will be really helpful information.  This box has devices with
RMRR records and if they're not set up correctly, DMAR faults can occur.

>>
>> We should also rate-limit DMA faults, which would avoid the lockup
>> failure mode. Bjorn, what should an IOMMU driver *do* when it detects
>> that a device is creating an endless stream of DMA faults and isn't
>> aborting the transaction?
> 
> You mentioned that POWER with EEH does something intelligent in this
> case, but I'm not familiar with that code.  We have AER support, which
> can result in resetting a device, but I think DMA faults are reported
> differently, and I don't think there's any nice existing way for PCI
> to deal with them.  Maybe there should be, though.
> 
> Bjorn
> _______________________________________________
> iommu mailing list
> iommu@...ts.linux-foundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/iommu
> 

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