Re: [PATCH 1/1] pci/quirks: fix a dmar fault for intel 82599 card

[Li, ZhenHua]

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-hual@xxxxxx> 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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