well, then I will create a patch for ALL pcie devices. On 10/03/2014 10:28 PM, Alexander Duyck wrote: > On 10/02/2014 08:09 AM, Bjorn Helgaas wrote: >> On Tue, Sep 30, 2014 at 12:15 AM, Li, ZhenHua <zhen-h...@hp.com> wrote: >>> Add Joerg to CC list. For it is also related to iommu module. >>> >>> Joerg, >>> There was a try for this dmar fault, >>> https://lkml.org/lkml/2014/8/18/118 >>> >>> This patch is trying to fix the same thing. >>> >>> >>> Zhenhua >>> >>> On 09/30/2014 02:09 PM, Li, Zhen-Hua wrote: >>>> On a HP system with Intel Corporation 82599 ethernet adapter, when kernel >>>> crashed and the kdump kernel boots with intel_iommu=on, there may be some >>>> unexpected DMA requests on this adapter, which will cause DMA Remapping >>>> faults like: >>>> dmar: DRHD: handling fault status reg 102 >>>> dmar: DMAR:[DMA Read] Request device [41:00.0] fault addr fff81000 >>>> DMAR:[fault reason 01] Present bit in root entry is clear >>>> >>>> Analysis for this bug: >>>> >>>> The present bit is set in this function: >>>> >>>> static struct context_entry * device_to_context_entry( >>>> struct intel_iommu *iommu, u8 bus, u8 devfn) >>>> { >>>> ...... >>>> set_root_present(root); >>>> ...... >>>> } >>>> >>>> Calling tree: >>>> ixgbe_open >>>> ixgbe_setup_tx_resources >>>> intel_alloc_coherent >>>> __intel_map_single >>>> domain_context_mapping >>>> domain_context_mapping_one >>>> device_to_context_entry >>>> >>>> This means, the present bit in root entry will not be set until the device >>>> driver is loaded. >>>> >>>> But in the kdump kernel, some hardware device does not know the OS is the >>>> second kernel and the drivers should be loaded again, this causes there >>>> are >>>> some unexpected DMA requsts on this device when it has not been >>>> initialized, >>>> and then the DMA Remapping errors come. >>>> >>>> To fix this DMAR fault, we need to reset the bus that this device on. >>>> Reset >>>> the device itself does not work. >> This seems like something that could happen with *any* device, not >> just the 82599 NIC. Or is there something in the "kernel crash -> >> kexec -> kdump kernel" path that stops DMA for most devices, but not >> for the 82599?lex >> > > This is an *any* device problem. Specifically any device that is doing > active DMA when a kdump kernel is triggered will cause this issue since > the IOMMU will not have valid mappings for the DMA events until the > device driver itself is loaded and resets the device. > > Thanks, > > Alex >
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