Subject: Re: [PATCH] powerpc/powernv: Fix IOMMU group lost

From: Wei Yang <[email-masked]>
Date: Wed, 6 Aug 2014 00:03:23 +0800

I just give a shot with patch on PHB3 with hotplug case. From the functional
point of view, it works. The iommu group is created and attached with device.
While it still has the problem we had which commit 3f28c5a tried to solve.

In the test case, the pci bus is not removed. This means in
pcibios_add_device(), it will try to add iommu group since the
pci_bus->is_added is true. And at this moment the pci_dev->kobj->sd is not
initialized properly. This makes the iommu_add_device() fail.

Your patch delete the warning at this place, so from the log it looks good. But
actually, it is not that clear to address the problem. We still have two
problems:
   1. iommu group will fail to be created
   2. iommu group will be created multiple times

My opinion is to make a clear understanding of the order/sequence of the iommu
group creation in both pci bus removed/not removed cases, than create and
attach it properly.

On Tue, Aug 05, 2014 at 06:27:38PM +1000, Gavin Shan wrote:
>When we take full hotplug to recover from EEH errors, PCI buses
>could be involved. For the case, the child devices of involved
>PCI buses can't be attached to IOMMU group properly, which is
>caused by commit 3f28c5a ("powerpc/powernv: Reduce multi-hit of
>iommu_add_device()").
>
>When adding the PCI devices of the newly created PCI buses to
>the system, the IOMMU group is expected to be added in (C).
>(A) fails to bind the IOMMU group because bus->is_added is
>false. (B) fails because the device doesn't have binding IOMMU
>table yet. bus->is_added is set to true at end of (C) and
>pdev->is_added is set to true at (D).
>
>   pcibios_add_pci_devices()
>      pci_scan_bridge()
>         pci_scan_child_bus()
>            pci_scan_slot()
>               pci_scan_single_device()
>                  pci_scan_device()
>                  pci_device_add()
>                     pcibios_add_device()           A: Ignore
>                     device_add()                   B: Ignore
>                  pcibios_fixup_bus()
>                     pcibios_setup_bus_devices()
>                        pcibios_setup_device()      C: Hit
>      pcibios_finish_adding_to_bus()
>         pci_bus_add_devices()
>            pci_bus_add_device()                    D: Add device
>
>If the parent PCI bus isn't involved in hotplug, the IOMMU
>group is expected to be bound in (A).
>
>The patch fixes the issue by reverting commit 3f28c5a and remove
>WARN_ON() in iommu_add_device() to allow calling the function
>even the specified device already has associated IOMMU group.
>
>Cc: <[email-masked]>  # 3.16+
>Reported-by: Thadeu Lima de Souza Cascardo <[email-masked]>
>Signed-off-by: Gavin Shan <[email-masked]>
>Tested-by: Wei Yang <[email-masked]>
>---
> arch/powerpc/kernel/iommu.c               | 30 +++++++++++++-----------------
> arch/powerpc/platforms/powernv/pci-ioda.c |  2 +-
> 2 files changed, 14 insertions(+), 18 deletions(-)
>
>diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>index 88e3ec6..4663c10 100644
>--- a/arch/powerpc/kernel/iommu.c
>+++ b/arch/powerpc/kernel/iommu.c
>@@ -1120,37 +1120,33 @@ EXPORT_SYMBOL_GPL(iommu_release_ownership);
> int iommu_add_device(struct device *dev)
> {
> 	struct iommu_table *tbl;
>-	int ret = 0;
>
>-	if (WARN_ON(dev->iommu_group)) {
>-		pr_warn("iommu_tce: device %s is already in iommu group %d, skipping\n",
>-				dev_name(dev),
>-				iommu_group_id(dev->iommu_group));
>+	if (dev->iommu_group) {
>+		pr_debug("%s: Skipping device %s with iommu group %d\n",
>+			 __func__, dev_name(dev),
>+			 iommu_group_id(dev->iommu_group));
> 		return -EBUSY;
> 	}
>
> 	tbl = get_iommu_table_base(dev);
> 	if (!tbl || !tbl->it_group) {
>-		pr_debug("iommu_tce: skipping device %s with no tbl\n",
>-				dev_name(dev));
>+		pr_debug("%s: Skipping device %s with no tbl\n",
>+			 __func__, dev_name(dev));
> 		return 0;
> 	}
>
>-	pr_debug("iommu_tce: adding %s to iommu group %d\n",
>-			dev_name(dev), iommu_group_id(tbl->it_group));
>+	pr_debug("%s: Adding %s to iommu group %d\n",
>+		 __func__, dev_name(dev),
>+		 iommu_group_id(tbl->it_group));
>
> 	if (PAGE_SIZE < IOMMU_PAGE_SIZE(tbl)) {
>-		pr_err("iommu_tce: unsupported iommu page size.");
>-		pr_err("%s has not been added\n", dev_name(dev));
>+		pr_err("%s: Invalid IOMMU page size %lx (%lx) on %s\n",
>+		       __func__, IOMMU_PAGE_SIZE(tbl),
>+		       PAGE_SIZE, dev_name(dev));
> 		return -EINVAL;
> 	}
>
>-	ret = iommu_group_add_device(tbl->it_group, dev);
>-	if (ret < 0)
>-		pr_err("iommu_tce: %s has not been added, ret=%d\n",
>-				dev_name(dev), ret);
>-
>-	return ret;
>+	return iommu_group_add_device(tbl->it_group, dev);
> }
> EXPORT_SYMBOL_GPL(iommu_add_device);
>
>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
>index de19ede..86290eb 100644
>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
>@@ -462,7 +462,7 @@ static void pnv_pci_ioda_dma_dev_setup(struct pnv_phb *phb, struct pci_dev *pdev
>
> 	pe = &phb->ioda.pe_array[pdn->pe_number];
> 	WARN_ON(get_dma_ops(&pdev->dev) != &dma_iommu_ops);
>-	set_iommu_table_base(&pdev->dev, &pe->tce32_table);
>+	set_iommu_table_base_and_group(&pdev->dev, &pe->tce32_table);
> }
>
> static int pnv_pci_ioda_dma_set_mask(struct pnv_phb *phb,
>-- 
>1.8.3.2

-- 
Richard Yang
Help you, Help me