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

["Li, ZhenHua" <zhen-hual@hp.com>]

On 10/17/2014 05:44 PM, 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>

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@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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