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Date:	Mon, 20 Oct 2014 10:19:12 +0800
From:	"Li, ZhenHua" <zhen-hual@...com>
To:	Takao Indoh <indou.takao@...fujitsu.com>
CC:	bhelgaas@...gle.com, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, linda.knippers@...com,
	jerry.hoemann@...com, lisa.mitchell@...com,
	alexander.duyck@...il.com, rwright@...com
Subject: Re: [PATCH 1/1] pci: fix dmar fault for kdump kernel

Hi  Takao Indoh,

According to this discussion
	https://lkml.org/lkml/2014/10/17/107

It seems that we can not do the resetting on the first kernel.  It can
only be called during kdump kernel boots.

Thanks
Zhenhua
On 10/15/2014 04:14 PM, Takao Indoh wrote:
> (2014/10/14 18:34), Li, ZhenHua wrote:
>> 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
> 
> As far as I can remember, the original patch was nacked by
> the following reasons:
> 
> 1) On sparc, the IOMMU is initialized before PCI devices are enumerated,
>     so there would still be a window where ongoing DMA could cause an
>     IOMMU error.
> 
> 2) Basically Bjorn is thinking device reset should be done in the
>     1st kernel before jumping into 2nd kernel.
> 
> And Bill Sumner proposed another idea.
> http://comments.gmane.org/gmane.linux.kernel.iommu/4828
> I don't know the current status of this patch, but I think Jerry Hoemann
> is working on this.
> 
> Thanks,
> Takao Indoh
> 
> 
>>>
>>> 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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