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Message-ID: <544617FC.1020300@jp.fujitsu.com>
Date: Tue, 21 Oct 2014 17:23:24 +0900
From: Takao Indoh <indou.takao@...fujitsu.com>
To: zhen-hual@...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 ZhenHua,
(2014/10/20 11:19), Li, ZhenHua wrote:
> 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.
Sounds like that. Do you know any example cases which cannot be fixed by
Bill's patch?
Thanks,
Takao Indoh
>
> 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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