On 30/05/18 14:12, Thierry Reding wrote:
On Wed, May 30, 2018 at 02:54:46PM +0200, Thierry Reding wrote:
On Wed, May 30, 2018 at 10:59:30AM +0100, Robin Murphy wrote:
On 30/05/18 09:03, Thierry Reding wrote:
From: Thierry Reding <treding@xxxxxxxxxx>
Implement this function to enable drivers from detaching from any IOMMU
domains that architecture code might have attached them to so that they
can take exclusive control of the IOMMU via the IOMMU API.
Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
Changes in v3:
- make API 32-bit ARM specific
- avoid extra local variable
Changes in v2:
- fix compilation
arch/arm/include/asm/dma-mapping.h | 3 +++
arch/arm/mm/dma-mapping-nommu.c | 4 ++++
arch/arm/mm/dma-mapping.c | 16 ++++++++++++++++
3 files changed, 23 insertions(+)
diff --git a/arch/arm/include/asm/dma-mapping.h b/arch/arm/include/asm/dma-mapping.h
index 8436f6ade57d..5960e9f3a9d0 100644
--- a/arch/arm/include/asm/dma-mapping.h
+++ b/arch/arm/include/asm/dma-mapping.h
@@ -103,6 +103,9 @@ extern void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
#define arch_teardown_dma_ops arch_teardown_dma_ops
extern void arch_teardown_dma_ops(struct device *dev);
+#define arm_dma_iommu_detach_device arm_dma_iommu_detach_device
+extern void arm_dma_iommu_detach_device(struct device *dev);
+
/* do not use this function in a driver */
static inline bool is_device_dma_coherent(struct device *dev)
{
diff --git a/arch/arm/mm/dma-mapping-nommu.c b/arch/arm/mm/dma-mapping-nommu.c
index f448a0663b10..eb781369377b 100644
--- a/arch/arm/mm/dma-mapping-nommu.c
+++ b/arch/arm/mm/dma-mapping-nommu.c
@@ -241,3 +241,7 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
void arch_teardown_dma_ops(struct device *dev)
{
}
+
+void arm_dma_iommu_detach_device(struct device *dev)
+{
+}
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index af27f1c22d93..6d8af08b3e7d 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -2400,3 +2400,19 @@ void arch_teardown_dma_ops(struct device *dev)
arm_teardown_iommu_dma_ops(dev);
}
+
+void arm_dma_iommu_detach_device(struct device *dev)
+{
+#ifdef CONFIG_ARM_DMA_USE_IOMMU
+ struct dma_iommu_mapping *mapping = to_dma_iommu_mapping(dev);
+
+ if (!mapping)
+ return;
+
+ arm_iommu_release_mapping(mapping);
Potentially freeing the mapping before you try to operate on it is never the
best idea. Plus arm_iommu_detach_device() already releases a reference
appropriately anyway, so it's a double-free.
But the reference released by arm_iommu_detach_device() is to balance
out the reference acquired by arm_iommu_attach_device(), isn't it? In
the above, the arm_iommu_release_mapping() is supposed to drop the
final reference which was obtained by arm_iommu_create_mapping(). The
mapping shouldn't go away irrespective of the order in which these
will be called.
Going over the DMA/IOMMU code I just remembered that I drew inspiration
from arm_teardown_iommu_dma_ops() for the initial proposal which also
calls both arm_iommu_detach_device() and arm_iommu_release_mapping().
That said, one other possibility to implement this would be to export
the 32-bit and 64-bit ARM implementations of arch_teardown_dma_ops()
and use that instead. linux/dma-mapping.h implements a stub for
architectures that don't provide one, so it should work without any
#ifdef guards.
That combined with the set_dma_ops() fix in arm_iommu_detach_device()
should fix this pretty nicely.
OK, having a second look at the ARM code I see I had indeed overlooked
that extra reference held until arm_teardown_iommu_dma_ops() - mea culpa
- but frankly that looks wrong anyway, as it basically defeats the point
of refcounting the mapping at all. AFAICS arm_setup_iommu_dma_ops()
should just be made to behave 'normally' by unconditionally dropping the
initial reference after calling __arm_iommu_attach_device(), then we
don't need all these odd and confusing release calls dotted around at all.
Robin.
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