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SubjectRe: [PATCH 1/1] pci: reset all pci endpoints to stop on going dma

On 10/20/2014 07:20 AM, Gavin Shan wrote:
> On Fri, Oct 17, 2014 at 02:44:43AM -0700, Eric W. Biederman wrote:
>> "Li, Zhen-Hua" <zhen-hual@hp.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@xmission.com>
>> Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
>> Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
>>
>> 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.
>>
>
> Zhenhua, Intrestingly, PPC has mechanism to reset the root port for kdump case
> in order to drop pending DMA traffic. Maybe you can implement similar thing.
> However, this kind of reset would be platform/board specific and needs support
> from underly firmware. More details could be found from arch/powerpc/
> platforms/powernv/pci-ioda.c
>
> if (is_kdump_kernel()) {
> pr_info(" Issue PHB reset ...\n");
> ioda_eeh_phb_reset(hose, EEH_RESET_FUNDAMENTAL);
> ioda_eeh_phb_reset(hose, OPAL_DEASSERT_RESET);
> }
>
> Please check if it's the thing you're looking for. I didn't understand your
> requirements 100%
>
> Thanks,
> Gavin
Gavin,
I was trying to fix a DMAR fault for iommu. On X86 platform, iommu is
initialized after pci , while on powerpc iommu is before pci. So I
tried to do the operation in the first kernel, and this can work on all
platforms.

But according to Eric's mail, it is inappropriate doing this in
crash_kexec. So I have to figure out how to do this in the kdump kernel.

As it is clear the powerpc has already do the resetting during booting,
so I only need to implement a similar mechanism on X86 system.

Thanks
Zhenhua
>
>> Eric
>>
>>
>>> 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@hp.com>
>>> Signed-off-by: Takao Indoh <indou.takao@jp.fujitsu.com>
>>> Signed-off-by: Randy Wright <rwright@hp.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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>>
>



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