[PATCH] iommu: Implement deferred domain attachment

Joerg Roedel joro at 8bytes.org
Fri May 15 16:14:00 UTC 2020


On Fri, May 15, 2020 at 04:42:23PM +0100, Robin Murphy wrote:
> >   struct iommu_domain *iommu_get_dma_domain(struct device *dev)
> >   {
> > -	return dev->iommu_group->default_domain;
> > +	struct iommu_domain *domain = dev->iommu_group->default_domain;
> > +
> > +	if (__iommu_is_attach_deferred(domain, dev))
> > +		__iommu_attach_device_no_defer(domain, dev);
> 
> This raises a red flag, since iommu-dma already has explicit deferred attach
> handling where it should need it, immediately after this is called to
> retrieve the domain. The whole thing smells to me like we should have an
> explicit special-case in iommu_probe_device() rather than hooking
> __iommu_attach_device() in general then having to bodge around the fallout
> elsewhere.

Good point, I missed that. But it didn't work for its only user, the
AMD IOMMU driver, the reason is that it calls iommu_attach_device(),
which in its code-path checks for deferred attaching again and bails
out, without do the real attachment.

But below updated fix should work. Jerry, could you please test it
again?

>From 4e262dedcd36c7572312c65e66416da74fc78047 Mon Sep 17 00:00:00 2001
From: Joerg Roedel <jroedel at suse.de>
Date: Fri, 15 May 2020 11:25:03 +0200
Subject: [PATCH] iommu: Fix deferred domain attachment

The IOMMU core code has support for deferring the attachment of a domain
to a device. This is needed in kdump kernels where the new domain must
not be attached to a device before the device driver takes it over.

When the AMD IOMMU driver got converted to use the dma-iommu
implementation, the deferred attaching got lost. The code in
dma-iommu.c has support for deferred attaching, but it calls into
iommu_attach_device() to actually do it. But iommu_attach_device()
will check if the device should be deferred in it code-path and do
nothing, breaking deferred attachment.

Provide a function in IOMMU core code to reliably attach a device to a
domain without any deferred checks and also without other safe-guards.

Cc: Jerry Snitselaar <jsnitsel at redhat.com>
Cc: Tom Murphy <murphyt7 at tcd.ie>
Reported-by: Jerry Snitselaar <jsnitsel at redhat.com>
Fixes: 795bbbb9b6f8 ("iommu/dma-iommu: Handle deferred devices")
Signed-off-by: Joerg Roedel <jroedel at suse.de>
---
 drivers/iommu/dma-iommu.c |  4 ++--
 drivers/iommu/iommu.c     | 37 ++++++++++++++++++++++++++++++++-----
 include/linux/iommu.h     |  2 ++
 3 files changed, 36 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index ba128d1cdaee..403fda04ea98 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -362,8 +362,8 @@ static int iommu_dma_deferred_attach(struct device *dev,
 		return 0;
 
 	if (unlikely(ops->is_attach_deferred &&
-			ops->is_attach_deferred(domain, dev)))
-		return iommu_attach_device(domain, dev);
+		     ops->is_attach_deferred(domain, dev)))
+		return iommu_attach_device_no_defer(domain, dev);
 
 	return 0;
 }
diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index 4050569188be..91dbdbc6d640 100644
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -23,6 +23,7 @@
 #include <linux/property.h>
 #include <linux/fsl/mc.h>
 #include <linux/module.h>
+#include <linux/crash_dump.h>
 #include <trace/events/iommu.h>
 
 static struct kset *iommu_group_kset;
@@ -1889,13 +1890,19 @@ void iommu_domain_free(struct iommu_domain *domain)
 }
 EXPORT_SYMBOL_GPL(iommu_domain_free);
 
-static int __iommu_attach_device(struct iommu_domain *domain,
-				 struct device *dev)
+static bool __iommu_is_attach_deferred(struct iommu_domain *domain,
+				       struct device *dev)
+{
+	if (!domain->ops->is_attach_deferred)
+		return false;
+
+	return domain->ops->is_attach_deferred(domain, dev);
+}
+
+static int __iommu_attach_device_no_defer(struct iommu_domain *domain,
+					  struct device *dev)
 {
 	int ret;
-	if ((domain->ops->is_attach_deferred != NULL) &&
-	    domain->ops->is_attach_deferred(domain, dev))
-		return 0;
 
 	if (unlikely(domain->ops->attach_dev == NULL))
 		return -ENODEV;
@@ -1903,9 +1910,29 @@ static int __iommu_attach_device(struct iommu_domain *domain,
 	ret = domain->ops->attach_dev(domain, dev);
 	if (!ret)
 		trace_attach_device_to_domain(dev);
+
 	return ret;
 }
 
+static int __iommu_attach_device(struct iommu_domain *domain,
+				 struct device *dev)
+{
+	if (__iommu_is_attach_deferred(domain, dev))
+		return 0;
+
+	return __iommu_attach_device_no_defer(domain, dev);
+}
+
+int iommu_attach_device_no_defer(struct iommu_domain *domain,
+				 struct device *dev)
+{
+	/* Safe-Guard to only call this when needed */
+	if (!is_kdump_kernel())
+		return -ENODEV;
+
+	return __iommu_attach_device_no_defer(domain, dev);
+}
+
 int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
 {
 	struct iommu_group *group;
diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 7cfd2dddb49d..f82b20a61d0b 100644
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -449,6 +449,8 @@ extern struct iommu_group *iommu_group_get_by_id(int id);
 extern void iommu_domain_free(struct iommu_domain *domain);
 extern int iommu_attach_device(struct iommu_domain *domain,
 			       struct device *dev);
+extern int iommu_attach_device_no_defer(struct iommu_domain *domain,
+					struct device *dev);
 extern void iommu_detach_device(struct iommu_domain *domain,
 				struct device *dev);
 extern int iommu_cache_invalidate(struct iommu_domain *domain,
-- 
2.25.1



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