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SubjectRe: 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
> <> 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 <>
>>>> 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

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