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Message-ID: <501F4877.5050605@jp.fujitsu.com>
Date: Mon, 06 Aug 2012 13:30:47 +0900
From: Takao Indoh <indou.takao@...fujitsu.com>
To: vgoyal@...hat.com
CC: kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
linux-pci@...r.kernel.org, bhelgaas@...gle.com, hbabu@...ibm.com,
ishii.hironobu@...fujitsu.com, martin.wilck@...fujitsu.com
Subject: Re: [RFC][PATCH] Reset PCIe devices to address DMA problem on kdump
with iommu
Hi Vivek,
(2012/08/03 20:46), Vivek Goyal wrote:
> On Fri, Aug 03, 2012 at 08:24:31PM +0900, Takao Indoh wrote:
>> Hi all,
>>
>> This patch adds kernel parameter "reset_pcie_devices" which resets PCIe
>> devices at boot time to address DMA problem on kdump with iommu. When
>> this parameter is specified, a hot reset is triggered on each PCIe root
>> port and downstream port to reset its downstream endpoint.
>
> Hi Takao,
>
> Why not use existing "reset_devices" parameter instead of introducing
> a new one?
"reset_devices" is used for each driver to reset their own device, and
this patch resets all devices forcibly, so I thought they were different
things.
Thanks,
Takao Indoh
>
> Thanks
> Vivek
>
>>
>> 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. Recently 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 address this problem DMA needs to be stopped before DMAR
>> is initialized at kdump kernel boot time. By this patch, PCIe devices
>> are reset by hot reset and its DMA is stopped when reset_pcie_devices is
>> specified. One problem of this solution is that VGA is reset and the
>> monitor blacks out when the link between the port and VGA controller was
>> reset. So this patch does not reset the port whose child endpoint is VGA
>> device.
>>
>> Any comments would be appreciated.
>>
>> Signed-off-by: Takao Indoh <indou.takao@...fujitsu.com>
>> ---
>> Documentation/kernel-parameters.txt | 4 +
>> drivers/pci/quirks.c | 59 ++++++++++++++++++++++++++
>> 2 files changed, 63 insertions(+)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index e714a02..e694e9f 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -2489,6 +2489,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>> reset_devices [KNL] Force drivers to reset the underlying device
>> during initialization.
>>
>> + reset_pcie_devices
>> + [PCIE] Reset PCIe endpoint at boot time by sending a
>> + hot reset to root port and downstream port
>> +
>> resume= [SWSUSP]
>> Specify the partition device for software suspend
>> Format:
>> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
>> index 5155317..7f7fc02 100644
>> --- a/drivers/pci/quirks.c
>> +++ b/drivers/pci/quirks.c
>> @@ -32,6 +32,65 @@
>> #include "pci.h"
>>
>> /*
>> + * Reset PCIe endpoint by sending a hot reset to root port and downstream port
>> + */
>> +unsigned int reset_pcie_devices;
>> +EXPORT_SYMBOL(reset_pcie_devices);
>> +static int __init set_reset_pcie_devices(char *str)
>> +{
>> + reset_pcie_devices = 1;
>> + return 1;
>> +}
>> +__setup("reset_pcie_devices", set_reset_pcie_devices);
>> +
>> +static void __devinit quirk_pcie_device_reset(struct pci_dev *dev)
>> +{
>> + struct pci_bus *subordinate;
>> + struct pci_dev *child;
>> + u16 ctrl;
>> +
>> + if (!reset_pcie_devices || !pci_is_pcie(dev) || !dev->subordinate ||
>> + ((dev->pcie_type != PCI_EXP_TYPE_ROOT_PORT) &&
>> + (dev->pcie_type != PCI_EXP_TYPE_DOWNSTREAM)))
>> + return;
>> +
>> + subordinate = dev->subordinate;
>> + list_for_each_entry(child, &subordinate->devices, bus_list) {
>> + if ((child->pcie_type == PCI_EXP_TYPE_UPSTREAM) ||
>> + (child->pcie_type == PCI_EXP_TYPE_PCI_BRIDGE) ||
>> + ((child->class >> 16) == PCI_BASE_CLASS_DISPLAY))
>> + /* Don't reset switch, bridge, VGA device */
>> + return;
>> + }
>> +
>> + dev_info(&dev->dev, "Reset Secondary bus\n");
>> +
>> + list_for_each_entry(child, &subordinate->devices, bus_list) {
>> + dev_info(&child->dev, "save state\n");
>> + pci_save_state(child);
>> + }
>> +
>> + /* Assert Secondary Bus Reset */
>> + pci_read_config_word(dev, PCI_BRIDGE_CONTROL, &ctrl);
>> + ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
>> + pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl);
>> +
>> + msleep(2);
>> +
>> + /* De-assert Secondary Bus Reset */
>> + ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
>> + pci_write_config_word(dev, PCI_BRIDGE_CONTROL, ctrl);
>> +
>> + msleep(200);
>> +
>> + list_for_each_entry(child, &subordinate->devices, bus_list) {
>> + dev_info(&child->dev, "restore state\n");
>> + pci_restore_state(child);
>> + }
>> +}
>> +DECLARE_PCI_FIXUP_FINAL(PCI_ANY_ID, PCI_ANY_ID, quirk_pcie_device_reset);
>> +
>> +/*
>> * Decoding should be disabled for a PCI device during BAR sizing to avoid
>> * conflict. But doing so may cause problems on host bridge and perhaps other
>> * key system devices. For devices that need to have mmio decoding always-on,
>
>
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