powerpc/iommu/powernv: Release replaced TCE

At the moment writing new TCE value to the IOMMU table fails with EBUSY
if there is a valid entry already. However PAPR specification allows
the guest to write new TCE value without clearing it first.

Another problem this patch is addressing is the use of pool locks for
external IOMMU users such as VFIO. The pool locks are to protect
DMA page allocator rather than entries and since the host kernel does
not control what pages are in use, there is no point in pool locks and
exchange()+put_page(oldtce) is sufficient to avoid possible races.

This adds an exchange() callback to iommu_table_ops which does the same
thing as set() plus it returns replaced TCE and DMA direction so
the caller can release the pages afterwards. The exchange() receives
a physical address unlike set() which receives linear mapping address;
and returns a physical address as the clear() does.

This implements exchange() for P5IOC2/IODA/IODA2. This adds a requirement
for a platform to have exchange() implemented in order to support VFIO.

This replaces iommu_tce_build() and iommu_clear_tce() with
a single iommu_tce_xchg().

This makes sure that TCE permission bits are not set in TCE passed to
IOMMU API as those are to be calculated by platform code from
DMA direction.

This moves SetPageDirty() to the IOMMU code to make it work for both
VFIO ioctl interface in in-kernel TCE acceleration (when it becomes
available later).

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
[aw: for the vfio related changes]
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 18 insertions, 4 deletions

diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
index 489133cf7c5e..4636734604d7 100644
--- a/arch/powerpc/include/asm/iommu.h
+++ b/arch/powerpc/include/asm/iommu.h
@@ -45,13 +45,29 @@ extern int iommu_is_off;
 extern int iommu_force_on;
 
 struct iommu_table_ops {
+	/*
+	 * When called with direction==DMA_NONE, it is equal to clear().
+	 * uaddr is a linear map address.
+	 */
 	int (*set)(struct iommu_table *tbl,
 			long index, long npages,
 			unsigned long uaddr,
 			enum dma_data_direction direction,
 			struct dma_attrs *attrs);
+#ifdef CONFIG_IOMMU_API
+	/*
+	 * Exchanges existing TCE with new TCE plus direction bits;
+	 * returns old TCE and DMA direction mask.
+	 * @tce is a physical address.
+	 */
+	int (*exchange)(struct iommu_table *tbl,
+			long index,
+			unsigned long *hpa,
+			enum dma_data_direction *direction);
+#endif
 	void (*clear)(struct iommu_table *tbl,
 			long index, long npages);
+	/* get() returns a physical address */
 	unsigned long (*get)(struct iommu_table *tbl, long index);
 	void (*flush)(struct iommu_table *tbl);
 };
@@ -153,6 +169,8 @@ extern void iommu_register_group(struct iommu_table_group *table_group,
 extern int iommu_add_device(struct device *dev);
 extern void iommu_del_device(struct device *dev);
 extern int __init tce_iommu_bus_notifier_init(void);
+extern long iommu_tce_xchg(struct iommu_table *tbl, unsigned long entry,
+		unsigned long *hpa, enum dma_data_direction *direction);
 #else
 static inline void iommu_register_group(struct iommu_table_group *table_group,
 					int pci_domain_number,
@@ -225,10 +243,6 @@ extern int iommu_tce_clear_param_check(struct iommu_table *tbl,
 		unsigned long npages);
 extern int iommu_tce_put_param_check(struct iommu_table *tbl,
 		unsigned long ioba, unsigned long tce);
-extern int iommu_tce_build(struct iommu_table *tbl, unsigned long entry,
-		unsigned long hwaddr, enum dma_data_direction direction);
-extern unsigned long iommu_clear_tce(struct iommu_table *tbl,
-		unsigned long entry);
 
 extern void iommu_flush_tce(struct iommu_table *tbl);
 extern int iommu_take_ownership(struct iommu_table *tbl);