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Date:	Tue, 14 Oct 2014 17:34:42 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org
CC:	"Li, Zhen-Hua" <zhen-hual@...com>, linda.knippers@...com,
	jerry.hoemann@...com, lisa.mitchell@...com,
	alexander.duyck@...il.com,
	Takao Indoh <indou.takao@...fujitsu.com>,
	Randy Wright <rwright@...com>
Subject: Re: [PATCH 1/1] pci: fix dmar fault for kdump kernel

I tested on the latest stable version 3.17, it works well.

On 10/10/2014 03:13 PM, Li, Zhen-Hua wrote:
> On a HP system with Intel vt-d supported and many PCI devices on it,
> 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
>
> This bug may happen on *any* PCI device.
> 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:
>      device driver
>          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, hardware devices are not aware that control has
> transferred to the second kernel, and those drivers must initialize again.
> Consequently there may be unexpected DMA requests from devices activity
> initiated in the first kernel leading to the DMA Remapping errors in the
> second kernel.
>
> To fix this DMAR fault, we need to reset the bus that this device on. Reset
> the device itself does not work.
>
> A patch for this bug that has been sent before:
> https://lkml.org/lkml/2014/9/30/55
> As in discussion, this bug may happen on *any* device, so we need to reset all
> pci devices.
>
> There was an original version(Takao Indoh) that resets the pcie devices:
> https://lkml.org/lkml/2013/5/14/9
>
> Update of this new version, comparing with Takao Indoh's version:
>      Add support for legacy PCI devices.
>      Use pci_try_reset_bus instead of do_downstream_device_reset in original version
>
> Randy Wright corrects some misunderstanding in this description.
>
> Signed-off-by: Li, Zhen-Hua <zhen-hual@...com>
> Signed-off-by: Takao Indoh <indou.takao@...fujitsu.com>
> Signed-off-by: Randy Wright <rwright@...com>
> ---
>   drivers/pci/pci.c | 84 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 84 insertions(+)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 2c9ac70..8cb146c 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -23,6 +23,7 @@
>   #include <linux/device.h>
>   #include <linux/pm_runtime.h>
>   #include <linux/pci_hotplug.h>
> +#include <linux/crash_dump.h>
>   #include <asm-generic/pci-bridge.h>
>   #include <asm/setup.h>
>   #include "pci.h"
> @@ -4423,6 +4424,89 @@ void __weak pci_fixup_cardbus(struct pci_bus *bus)
>   }
>   EXPORT_SYMBOL(pci_fixup_cardbus);
>
> +/*
> + * Return true if dev is PCI root port or downstream port whose child is PCI
> + * endpoint except VGA device.
> + */
> +static int __pci_dev_need_reset(struct pci_dev *dev)
> +{
> +	struct pci_bus *subordinate;
> +	struct pci_dev *child;
> +
> +	if (dev->hdr_type != PCI_HEADER_TYPE_BRIDGE)
> +		return 0;
> +
> +	if (pci_is_pcie(dev)) {
> +		if ((pci_pcie_type(dev) != PCI_EXP_TYPE_ROOT_PORT) &&
> +		    (pci_pcie_type(dev) != PCI_EXP_TYPE_DOWNSTREAM))
> +			return 0;
> +	}
> +
> +	subordinate = dev->subordinate;
> +	list_for_each_entry(child, &subordinate->devices, bus_list) {
> +		/* Don't reset switch, bridge, VGA device */
> +		if ((child->hdr_type == PCI_HEADER_TYPE_BRIDGE) ||
> +		    ((child->class >> 16) == PCI_BASE_CLASS_BRIDGE) ||
> +		    ((child->class >> 16) == PCI_BASE_CLASS_DISPLAY))
> +			return 0;
> +
> +		if (pci_is_pcie(child)) {
> +			if ((pci_pcie_type(child) == PCI_EXP_TYPE_UPSTREAM) ||
> +			    (pci_pcie_type(child) == PCI_EXP_TYPE_PCI_BRIDGE))
> +				return 0;
> +		}
> +	}
> +
> +	return 1;
> +}
> +
> +struct pci_dev_reset_entry {
> +	struct list_head list;
> +	struct pci_dev *dev;
> +};
> +int __init pci_reset_endpoints(void)
> +{
> +	struct pci_dev *dev = NULL;
> +	struct pci_dev_reset_entry *pdev_entry, *tmp;
> +	struct pci_bus *subordinate = NULL;
> +	int has_it;
> +
> +	LIST_HEAD(pdev_list);
> +
> +	if (likely(!is_kdump_kernel()))
> +		return 0;
> +
> +	for_each_pci_dev(dev) {
> +		subordinate = dev->subordinate;
> +		if (!subordinate || list_empty(&subordinate->devices))
> +			continue;
> +
> +		has_it = 0;
> +		list_for_each_entry(pdev_entry, &pdev_list, list) {
> +			if (dev == pdev_entry->dev) {
> +				has_it = 1;
> +				break;
> +			}
> +		}
> +		if (has_it)
> +			continue;
> +
> +		if (__pci_dev_need_reset(dev)) {
> +			pdev_entry = kmalloc(sizeof(*pdev_entry), GFP_KERNEL);
> +			pdev_entry->dev = dev;
> +			list_add(&pdev_entry->list, &pdev_list);
> +		}
> +	}
> +
> +	list_for_each_entry_safe(pdev_entry, tmp, &pdev_list, list) {
> +		pci_try_reset_bus(pdev_entry->dev->subordinate);
> +		kfree(pdev_entry);
> +	}
> +
> +	return 0;
> +}
> +fs_initcall_sync(pci_reset_endpoints);
> +
>   static int __init pci_setup(char *str)
>   {
>   	while (str) {
>

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