Patchwork iommu/vt-d: Handle hotplug devices' default identity mapping setting

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Submitter Lu Baolu
Date Feb. 24, 2019, 8:51 a.m.
Message ID <897e8383-ad75-35d0-5ad9-3d3a8b46b6ba@linux.intel.com>
Download mbox | patch
Permalink /patch/734675/
State New
Headers show

Comments

Lu Baolu - Feb. 24, 2019, 8:51 a.m.
Hi James,

On 2/22/19 3:36 PM, James Dong wrote:
> Baolu:
> 
> Sorry that my last reply email seems not text format. Resend it now.
> 
> Thanks for your comments and your patch. Please find below our responses to
> each of your comments:
> 
>> What does "I/O operation won't work" exactly mean here? Do you see any
>> IOMMU fault message? Or, something doesn't work as expected?
> 
> Yes, DMAR fault messages as following came out:
> [  354.939896] DMAR: DMAR:[DMA Read] Request device [03:00.1]fault addr 1fdfe80000
> [  354.939896] DMAR:[fault reason 02] Present bit in context entry is clear
> 
> 
>> Do you mind checking this?
>>
>> index 6ecdcf8fc8c0..f62f30bc1339 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -2632,6 +2632,9 @@ static struct dmar_domain
>> *find_or_alloc_domain(struct device *dev, int gaw)
>>                           goto out;
>>           }
>>
>> +       if (!iommu_should_identity_map(dev, 0))
>> +               return si_domain;
>> +
>>           /* Allocate and initialize new domain for the device */
>>           domain = alloc_domain(0);
>>           if (!domain)
> 
> Tried this patch, and the same DMAR fault message came out.

Thank you!

> 
> Guess it is because of the iommu code path for hotplug devices. If a hotplug
> device is rescanned after removal, iommu_bus_notifier will be called as part
> of the notifier chains to handle BUS_NOTIFY_ADD_DEVICE event. Along the code
> path, intel_iommu_ops->add_device() created an iommu group for this hotplug
> device, but failed to create an iommu domain because of the default domain
> type IOMMU_DOMAIN_IDENTITY imposed by current IOMMU command line option got
> declined by intel_iommu_ops->domain_alloc().

The Intel IOMMU driver hasn't switched to default domain yet although
it's in the pipe line. So, there should be no domain allocated when a
group is allocated for the device.

The problem is we need to check whether a hot-added device requires
identity map instead of allocating a normal domain blindly.

> 
> Since si_domain is type of "struct dmar_domain", which is platform dependent,
> it is hard to make this change in intel_iommu_ops->domain_alloc().
> 
> In your patch, function find_or_alloc_domain() is not in the code path of
> BUS_NOTIFY_ADD_DEVICE event notifier chain.
> 
> Please let us know if your have more concerns and suggestions.

Can you please try the patch attached? I think this is a generic issue
as I described in the commit message.

Best regards,
Lu Baolu
Benjamin Serebrin via iommu - Feb. 24, 2019, 4:10 p.m.
Baolu:

Yes, it is a generic issue for hotplug devices with current Intel IOMMU driver,
as reported in this thread as well.

The patch you provided does the job in our case. Please update this thread once
your patch is merged. Thanks.

Best Regards,
James

On 2/23/19 12:56 AM, Lu Baolu wrote
>
> @@ -4807,16 +4807,19 @@ static int device_notifier(struct notifier_block *nb,
> 	if (iommu_dummy(dev))
> 		return 0;
> 
>-	if (action != BUS_NOTIFY_REMOVED_DEVICE)
>-		return 0;
>-
>-	domain = find_domain(dev);
>-	if (!domain)
>-		return 0;
>+	if (action == BUS_NOTIFY_REMOVED_DEVICE) {
>+		domain = find_domain(dev);
>+		if (!domain)
>+			return 0;
> 
>-	dmar_remove_one_dev_info(dev);
>-	if (!domain_type_is_vm_or_si(domain) && list_empty(&domain->devices))
>-		domain_exit(domain);
>+		dmar_remove_one_dev_info(dev);
>+		if (!domain_type_is_vm_or_si(domain) &&
>+		    list_empty(&domain->devices))
>+			domain_exit(domain);
>+	} else if (action == BUS_NOTIFY_ADD_DEVICE) {
>+		if (iommu_should_identity_map(dev, 1))
>+			domain_add_dev_info(si_domain, dev);
>+	}

Patch

From d942e60557fc7ea6fee535fb9a0a7d334d65b636 Mon Sep 17 00:00:00 2001
From: Lu Baolu <baolu.lu@linux.intel.com>
Date: Sun, 24 Feb 2019 10:01:03 +0800
Subject: [PATCH 1/1] iommu/vt-d: Check identity map for hot-added devices

The Intel IOMMU driver will put devices into a static identity
mapped domain during boot if the kernel parameter "iommu=pt" is
used. That means the IOMMU hardware will translate a DMA address
into the same memory address.

Unfortunately, a hot-added device doesn't subject to this. That
results in some devices not working properly after hot added. A
quick way to reproduce this issue is to boot a system with

    iommu=pt

and, remove then readd the pci device with

    echo 1 > /sys/bus/pci/devices/[pci_source_id]/remove
    echo 1 > /sys/bus/pci/rescan

You will find the identity mapped domain was replaced with a
normal domain.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel-iommu.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 6ecdcf8fc8c0..730ee29d561b 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -3001,9 +3001,9 @@  static int iommu_should_identity_map(struct device *dev, int startup)
 	}
 
 	/*
-	 * At boot time, we don't yet know if devices will be 64-bit capable.
-	 * Assume that they will — if they turn out not to be, then we can
-	 * take them out of the 1:1 domain later.
+	 * At boot time or hot added, we don't yet know if devices will be
+	 * 64-bit capable. Assume that they will — if they turn out not to
+	 * be, then we can take them out of the 1:1 domain later.
 	 */
 	if (!startup) {
 		/*
@@ -4807,16 +4807,19 @@  static int device_notifier(struct notifier_block *nb,
 	if (iommu_dummy(dev))
 		return 0;
 
-	if (action != BUS_NOTIFY_REMOVED_DEVICE)
-		return 0;
-
-	domain = find_domain(dev);
-	if (!domain)
-		return 0;
+	if (action == BUS_NOTIFY_REMOVED_DEVICE) {
+		domain = find_domain(dev);
+		if (!domain)
+			return 0;
 
-	dmar_remove_one_dev_info(dev);
-	if (!domain_type_is_vm_or_si(domain) && list_empty(&domain->devices))
-		domain_exit(domain);
+		dmar_remove_one_dev_info(dev);
+		if (!domain_type_is_vm_or_si(domain) &&
+		    list_empty(&domain->devices))
+			domain_exit(domain);
+	} else if (action == BUS_NOTIFY_ADD_DEVICE) {
+		if (iommu_should_identity_map(dev, 1))
+			domain_add_dev_info(si_domain, dev);
+	}
 
 	return 0;
 }
-- 
2.17.1