Date:	Wed, 31 Jul 2013 09:35:24 +0900
From:	Takao Indoh <indou.takao@...fujitsu.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Vivek Goyal <vgoyal@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux-foundation.org>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"ishii.hironobu@...fujitsu.com" <ishii.hironobu@...fujitsu.com>,
	Don Dutile <ddutile@...hat.com>,
	"Sumner, William" <bill.sumner@...com>,
	"alex.williamson@...hat.com" <alex.williamson@...hat.com>,
	Haren Myneni <hbabu@...ibm.com>
Subject: Re: [PATCH v2] PCI: Reset PCIe devices to stop ongoing DMA

(2013/07/31 0:59), Bjorn Helgaas wrote:
> On Tue, Jul 30, 2013 at 12:09 AM, Takao Indoh
> <indou.takao@...fujitsu.com> wrote:
>> (2013/07/29 23:17), Bjorn Helgaas wrote:
>>> On Sun, Jul 28, 2013 at 6:37 PM, Takao Indoh <indou.takao@...fujitsu.com> wrote:
>>>> (2013/07/26 2:00), Bjorn Helgaas wrote:
> 
>>>>> My point about IOMMU and PCI initialization order doesn't go away just
>>>>> because it doesn't fit "kdump policy."  Having system initialization
>>>>> occur in a logical order is far more important than making kdump work.
>>>>
>>>> My next plan is as follows. I think this is matched to logical order
>>>> on boot.
>>>>
>>>> drivers/pci/pci.c
>>>> - Add function to reset bus, for example, pci_reset_bus(struct pci_bus *bus)
>>>>
>>>> drivers/iommu/intel-iommu.c
>>>> - On initialization, if IOMMU is already enabled, call this bus reset
>>>>     function before disabling and re-enabling IOMMU.
>>>
>>> I raised this issue because of arches like sparc that enumerate the
>>> IOMMU before the PCI devices that use it.  In that situation, I think
>>> you're proposing this:
>>>
>>>     panic kernel
>>>       enable IOMMU
>>>       panic
>>>     kdump kernel
>>>       initialize IOMMU (already enabled)
>>>         pci_reset_bus
>>>         disable IOMMU
>>>         enable IOMMU
>>>       enumerate PCI devices
>>>
>>> But the problem is that when you call pci_reset_bus(), you haven't
>>> enumerated the PCI devices, so you don't know what to reset.
>>
>> Right, so my idea is adding reset code into "intel-iommu.c". intel-iommu
>> initialization is based on the assumption that enumeration of PCI devices
>> is already done. We can find target device from IOMMU page table instead
>> of scanning all devices in pci tree.
>>
>> Therefore, this idea is only for intel-iommu. Other architectures need
>> to implement their own reset code.
> 
> That's my point.  I'm opposed to adding code to PCI when it only
> benefits x86 and we know other arches will need a fundamentally
> different design.  I would rather have a design that can work for all
> arches.
> 
> If your implementation is totally implemented under arch/x86 (or in
> intel-iommu.c, I guess), I can't object as much.  However, I think
> that eventually even x86 should enumerate the IOMMUs via ACPI before
> we enumerate PCI devices.
> 
> It's pretty clear that's how BIOS designers expect the OS to work.
> For example, sec 8.7.3 of the Intel Virtualization Technology for
> Directed I/O spec, rev 1.3, shows the expectation that remapping
> hardware (IOMMU) is initialized before discovering the I/O hierarchy
> below a hot-added host bridge.  Obviously you're not talking about a
> hot-add scenario, but I think the same sequence should apply at
> boot-time as well.

Of course I won't add something just for x86 into common PCI layer. I
attach my new patch, though it is not well tested yet.

On x86, currently IOMMU initialization run *after* PCI enumeration, but
what you are talking about is that it should be changed so that x86
IOMMU initialization is done *before* PCI enumeration like sparc, right?

Hmm, ok, I think I need to post attached patch to iommu list and
discuss it including current order of x86 IOMMU initialization.

Thanks,
Takao Indoh
---
 drivers/iommu/intel-iommu.c |   55 +++++++++++++++++++++++++++++++++-
 drivers/pci/pci.c           |   53 ++++++++++++++++++++++++++++++++
 include/linux/pci.h         |    1
 3 files changed, 108 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index eec0d3e..fb8a546 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3663,6 +3663,56 @@ static struct notifier_block device_nb = {
 	.notifier_call = device_notifier,
 };
 
+/* Reset PCI device if its entry exists in DMAR table */
+static void __init iommu_reset_devices(struct intel_iommu *iommu, u16 segment)
+{
+	u64 addr;
+	struct root_entry *root;
+	struct context_entry *context;
+	int bus, devfn;
+	struct pci_dev *dev;
+
+	addr = dmar_readq(iommu->reg + DMAR_RTADDR_REG);
+	if (!addr)
+		return;
+
+	/*
+	 *  In the case of kdump, ioremap is needed because root-entry table
+	 *  exists in first kernel's memory area which is not mapped in second
+	 *  kernel
+	 */
+	root = (struct root_entry*)ioremap(addr, PAGE_SIZE);
+	if (!root)
+		return;
+
+	for (bus=0; bus<ROOT_ENTRY_NR; bus++) {
+		if (!root_present(&root[bus]))
+			continue;
+
+		context = (struct context_entry *)ioremap(
+			root[bus].val & VTD_PAGE_MASK, PAGE_SIZE);
+		if (!context)
+			continue;
+
+		for (devfn=0; devfn<ROOT_ENTRY_NR; devfn++) {
+			if (!context_present(&context[devfn]))
+				continue;
+
+			dev = pci_get_domain_bus_and_slot(segment, bus, devfn);
+			if (!dev)
+				continue;
+
+			if (!pci_reset_bus(dev->bus)) /* go to next bus */
+				break;
+			else /* Try per-function reset */
+				pci_reset_function(dev);
+
+		}
+		iounmap(context);
+	}
+	iounmap(root);
+}
+
 int __init intel_iommu_init(void)
 {
 	int ret = 0;
@@ -3687,8 +3737,11 @@ int __init intel_iommu_init(void)
 			continue;
 
 		iommu = drhd->iommu;
-		if (iommu->gcmd & DMA_GCMD_TE)
+		if (iommu->gcmd & DMA_GCMD_TE) {
+			if (reset_devices)
+				iommu_reset_devices(iommu, drhd->segment);
 			iommu_disable_translation(iommu);
+		}
 	}
 
 	if (dmar_dev_scope_init() < 0) {
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index e37fea6..c595997 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -3392,6 +3392,59 @@ int pci_reset_function(struct pci_dev *dev)
 EXPORT_SYMBOL_GPL(pci_reset_function);
 
 /**
+ * pci_reset_bus - reset a PCI bus
+ * @bus: PCI bus to reset
+ *
+ * Returns 0 if the bus was successfully reset or negative if failed.
+ */
+int pci_reset_bus(struct pci_bus *bus)
+{
+	struct pci_dev *pdev;
+	u16 ctrl;
+
+	if (!bus->self)
+		return -ENOTTY;
+
+	list_for_each_entry(pdev, &bus->devices, bus_list)
+		if (pdev->subordinate)
+			return -ENOTTY;
+
+	/* Save config registers of children */
+	list_for_each_entry(pdev, &bus->devices, bus_list) {
+		dev_info(&pdev->dev, "Save state\n");
+		pci_save_state(pdev);
+	}
+
+	dev_info(&bus->self->dev, "Reset Secondary bus\n");
+
+	/* Assert Secondary Bus Reset */
+	pci_read_config_word(bus->self, PCI_BRIDGE_CONTROL, &ctrl);
+	ctrl |= PCI_BRIDGE_CTL_BUS_RESET;
+	pci_write_config_word(bus->self, PCI_BRIDGE_CONTROL, ctrl);
+
+	/* Read config again to flush previous write */
+	pci_read_config_word(bus->self, PCI_BRIDGE_CONTROL, &ctrl);
+
+	msleep(2);
+
+	/* De-assert Secondary Bus Reset */
+	ctrl &= ~PCI_BRIDGE_CTL_BUS_RESET;
+	pci_write_config_word(bus->self, PCI_BRIDGE_CONTROL, ctrl);
+
+	/* Wait for completion */
+	msleep(1000);
+
+	/* Restore config registers of children */
+	list_for_each_entry(pdev, &bus->devices, bus_list) {
+		dev_info(&pdev->dev, "Restore state\n");
+		pci_restore_state(pdev);
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pci_reset_bus);
+
+/**
  * pcix_get_max_mmrbc - get PCI-X maximum designed memory read byte count
  * @dev: PCI device to query
  *
diff --git a/include/linux/pci.h b/include/linux/pci.h
index 0fd1f15..125fbc6 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -924,6 +924,7 @@ int pcie_set_mps(struct pci_dev *dev, int mps);
 int __pci_reset_function(struct pci_dev *dev);
 int __pci_reset_function_locked(struct pci_dev *dev);
 int pci_reset_function(struct pci_dev *dev);
+int pci_reset_bus(struct pci_bus *bus);
 void pci_update_resource(struct pci_dev *dev, int resno);
 int __must_check pci_assign_resource(struct pci_dev *dev, int i);
 int __must_check pci_reassign_resource(struct pci_dev *dev, int i, resource_size_t add_size, resource_size_t align);

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