[PATCH v7 0/5] Reset PCIe devices to address DMA problem on kdump with iommu

MUNEDA Takahiro muneda.takahiro at jp.fujitsu.com
Fri Nov 30 10:49:05 EST 2012

On Tue, 27 Nov 2012 09:42:20 +0900 (JST),
Takao Indoh <indou.takao at jp.fujitsu.com> wrote:

> These patches reset PCIe devices at boot time to address DMA problem on
> kdump with iommu. When "reset_devices" is specified, a hot reset is
> triggered on each PCIe root port and downstream port to reset its
> downstream endpoint.
> Background:
> A kdump problem about DMA has been discussed for a long time. That is,
> when a kernel is switched to the kdump kernel, DMA derived from first
> kernel affects second kernel. Especially this problem surfaces when
> iommu is used for PCI passthrough on KVM guest. In the case of the
> machine I use, when intel_iommu=on is specified, DMAR error is detected
> in kdump kernel and PCI SERR is also detected. Finally kdump fails
> because some devices does not work correctly.
> The root cause is that ongoing DMA from first kernel causes DMAR fault
> because page table of DMAR is initialized while kdump kernel is booting
> up. Therefore to solve this problem DMA needs to be stopped before DMAR
> is initialized at kdump kernel boot time. By these patches, PCIe devices
> are reset by hot reset and its DMA is stopped when reset_devices is
> specified. One problem of this solution is that the monitor blacks out
> when VGA controller is reset. So this patch does not reset the port
> whose child endpoint is VGA device.
> What I tried:
> - Clearing bus master bit and INTx disable bit at boot time
>      This did not solve this problem. I still got DMAR error on devices.
> - Resetting devices in fixup_final(v1 patch)
>      DMAR error disappeared, but sometimes PCI SERR was detected. This
>      is well explained here.
>      https://lkml.org/lkml/2012/9/9/245
>      This PCI SERR seems to be related to interrupt remapping.
> - Clearing bus master in setup_arch() and resetting devices in
>    fixup_final
>      Neither DMAR error nor PCI SERR occurred. But on certain machine
>      kdump kernel hung up when resetting devices. It seems to be a
>      problem specific to the platform.
> - Resetting devices in setup_arch() (v2 and later patch)
>      This solution solves all problems I found so far.

Thank you for updating a patchset.
I have a server which raises PCI Error while system is rebooting when
I set intel_iommu=on.  With v7 on top of 3.7-rc7, I don't see any PCI
Errors or other hardware related errors. So,

Tested-by: MUNEDA Takahiro <muneda.takahiro at jp.fujitsu.com>


> Changelog:
> v7:
> Update Yinghai's dummy-pci patch with macros in linux/pci.h, and fix
> some bugs
> v6:
> Rewrite using Yinghai's dummy-pci patch
> https://lkml.org/lkml/2012/11/13/118
> v5:
> Do bus reset after all devices are scanned and its config registers are
> saved. This fixes a bug that config register is accessed without delay
> after reset.
> https://lkml.org/lkml/2012/10/17/47
> v4:
> Reduce waiting time after resetting devices. A previous patch does reset
> like this:
>    for (each device) {
>      save config registers
>      reset
>      wait for 500 ms
>      restore config registers
>    }
> If there are N devices to be reset, it takes N*500 ms. On the other
> hand, the v4 patch does:
>    for (each device) {
>      save config registers
>      reset
>    }
>    wait 500 ms
>    for (each device) {
>      restore config registers
>    }
> Though it needs more memory space to save config registers, the waiting
> time is always 500ms.
> https://lkml.org/lkml/2012/10/15/49
> v3:
> Move alloc_bootmem and free_bootmem to early_reset_pcie_devices so that
> they are called only once.
> https://lkml.org/lkml/2012/10/10/57
> v2:
> Reset devices in setup_arch() because reset need to be done before
> interrupt remapping is initialized.
> https://lkml.org/lkml/2012/10/2/54
> v1:
> Add fixup_final quirk to reset PCIe devices
> https://lkml.org/lkml/2012/8/3/160
> Takao Indoh (5):
>    x86, pci: add dummy pci device for early stage
>    PCI: Define the maximum number of PCI function
>    Make reset_devices available at early stage
>    x86, pci: Reset PCIe devices at boot time
>    x86, pci: Enable PCI INTx when MSI is disabled
>   arch/x86/include/asm/pci-direct.h |    3 +
>   arch/x86/kernel/setup.c           |    3 +
>   arch/x86/pci/common.c             |    4 +-
>   arch/x86/pci/early.c              |  315 +++++++++++++++++++++++++++++++++++++
>   include/linux/pci.h               |    2 +
>   init/main.c                       |    4 +-
>   6 files changed, 328 insertions(+), 3 deletions(-)
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