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Message-ID: <54446688.2060305@hp.com>
Date: Mon, 20 Oct 2014 09:34:00 +0800
From: "Li, ZhenHua" <zhen-hual@...com>
To: "Eric W. Biederman" <ebiederm@...ssion.com>
CC: linux-kernel@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
linux-pci@...r.kernel.org, indou.takao@...fujitsu.com,
kexec@...ts.infradead.org, linda.knippers@...com,
Randy Wright <rwright@...com>
Subject: Re: [PATCH 1/1] pci: reset all pci endpoints to stop on going dma
On 10/17/2014 05:44 PM, Eric W. Biederman wrote:
> "Li, Zhen-Hua" <zhen-hual@...com> writes:
>
>> This is an update of the patch
>> https://lkml.org/lkml/2014/10/10/37
>>
>> This patch is doing the reset works before the kdump kernel boots.
>
> If I have said it once I have said it a thousand times.
>
> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
> Nacked-by: "Eric W. Biederman" <ebiederm@...ssion.com>
I am very sorry for your name. I got your name by running the script
./scripts/get_maintainer.pl, maybe you need to update your name in the
git system.
>
> It is absolutely inappropriate to do this in the kernel that has
> crashed.
>
> Either reserve a chunk of the iommu for use by the crash dump kernel,
> or figure out how to do this during boot up.
>
> But this is absolutely and totally inappropriate to do in crash_kexec.
> The failure modes are all wrong. It will impact the reliability of our
> crash dumps.
>
> If an the code for a linux architecture is not structured in such a way
> as to make it easy or straight forward to do this my sympathies you are
> going to have do fix that linux port to be able to do things during
> boot.
>
> But things called from crash_kexec should be absolute necessities and I
> do not see this as coming anywhere close to being something that is
> impossible to do in the target kernel.
>
> Eric
>
So now do the resetting during the kdump kernel boots is the only
choice. I will try to figure out how to fix this.
Thank you very much.
Zhenhua
>
>> On a Linux system with iommu 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
>>
>> According to the previous discussion, On sparc, the IOMMU is initialized
>> before PCI devices are enumerated, this patch does the resetting works before
>> the kdump kernel boots, so it can also fix the problems on sparc.
>>
>> 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.
>> Reset all PCI/PCIe deviecs in the first kernel, before kdump kernel boots.
>>
>> 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 | 82 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>> include/linux/pci.h | 6 ++++
>> kernel/kexec.c | 2 ++
>> 3 files changed, 90 insertions(+)
>>
>> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
>> index 625a4ac..aa9192a 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"
>> @@ -4466,6 +4467,87 @@ 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 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);
>> +
>> +
>> + 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;
>> +}
>> +EXPORT_SYMBOL_GPL(pci_reset_endpoints);
>> +
>> static int __init pci_setup(char *str)
>> {
>> while (str) {
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 5be8db4..1cf7207 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -1869,4 +1869,10 @@ static inline bool pci_is_dev_assigned(struct pci_dev *pdev)
>> {
>> return (pdev->dev_flags & PCI_DEV_FLAGS_ASSIGNED) == PCI_DEV_FLAGS_ASSIGNED;
>> }
>> +
>> +/*
>> + * Reset all pci devices by resetting the buses.
>> + */
>> +int pci_reset_endpoints(void);
>> +
>> #endif /* LINUX_PCI_H */
>> diff --git a/kernel/kexec.c b/kernel/kexec.c
>> index 2abf9f6..986e8f7 100644
>> --- a/kernel/kexec.c
>> +++ b/kernel/kexec.c
>> @@ -36,6 +36,7 @@
>> #include <linux/syscore_ops.h>
>> #include <linux/compiler.h>
>> #include <linux/hugetlb.h>
>> +#include <linux/pci.h>
>>
>> #include <asm/page.h>
>> #include <asm/uaccess.h>
>> @@ -1474,6 +1475,7 @@ void crash_kexec(struct pt_regs *regs)
>> if (kexec_crash_image) {
>> struct pt_regs fixed_regs;
>>
>> + pci_reset_endpoints();
>> crash_setup_regs(&fixed_regs, regs);
>> crash_save_vmcoreinfo();
>> machine_crash_shutdown(&fixed_regs);
--
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