Add more detail to the documentation for memory_region_init_iommu()
and other IOMMU-related functions and data structures.
Signed-off-by: Peter Maydell <peter.mayd...@linaro.org>
---
v2->v3 changes:
* minor wording tweaks per Eric's review
* moved the bit about requirements to notify out from the translate
method docs to the top level class doc comment
* added description of flags argument and in particular that it's
just an optimization and callers can pass IOMMU_NONE to get the
full permissions
v1 -> v2 changes:
* documented replay method
* added note about wanting RCU or big qemu lock while calling
translate
---
include/exec/memory.h | 105 ++++++++++++++++++++++++++++++++++++++----
1 file changed, 95 insertions(+), 10 deletions(-)
diff --git a/include/exec/memory.h b/include/exec/memory.h
index 4fa1227f13..cce355d2d8 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -194,29 +194,100 @@ enum IOMMUMemoryRegionAttr {
IOMMU_ATTR_SPAPR_TCE_FD
};
+/**
+ * IOMMUMemoryRegionClass:
+ *
+ * All IOMMU implementations need to subclass TYPE_IOMMU_MEMORY_REGION
+ * and provide an implementation of at least the @translate method here
+ * to handle requests to the memory region. Other methods are optional.
+ *
+ * The IOMMU implementation must use the IOMMU notifier infrastructure
+ * to report whenever mappings are changed, by calling
+ * memory_region_notify_iommu() (or, if necessary, by calling
+ * memory_region_notify_one() for each registered notifier).
+ */
typedef struct IOMMUMemoryRegionClass {
/* private */
struct DeviceClass parent_class;
/*
- * Return a TLB entry that contains a given address. Flag should
- * be the access permission of this translation operation. We can
- * set flag to IOMMU_NONE to mean that we don't need any
- * read/write permission checks, like, when for region replay.
+ * Return a TLB entry that contains a given address.
+ *
+ * The IOMMUAccessFlags indicated via @flag are optional and may
+ * be specified as IOMMU_NONE to indicate that the caller needs
+ * the full translation information for both reads and writes. If
+ * the access flags are specified then the IOMMU implementation
+ * may use this as an optimization, to stop doing a page table
+ * walk as soon as it knows that the requested permissions are not
+ * allowed. If IOMMU_NONE is passed then the IOMMU must do the
+ * full page table walk and report the permissions in the returned
+ * IOMMUTLBEntry. (Note that this implies that an IOMMU may not
+ * return different mappings for reads and writes.)
+ *
+ * The returned information remains valid while the caller is
+ * holding the big QEMU lock or is inside an RCU critical section;
+ * if the caller wishes to cache the mapping beyond that it must
+ * register an IOMMU notifier so it can invalidate its cached
+ * information when the IOMMU mapping changes.
+ *
+ * @iommu: the IOMMUMemoryRegion
+ * @hwaddr: address to be translated within the memory region
+ * @flag: requested access permissions
*/
IOMMUTLBEntry (*translate)(IOMMUMemoryRegion *iommu, hwaddr addr,
IOMMUAccessFlags flag);
- /* Returns minimum supported page size */
+ /* Returns minimum supported page size in bytes.
+ * If this method is not provided then the minimum is assumed to
+ * be TARGET_PAGE_SIZE.
+ *
+ * @iommu: the IOMMUMemoryRegion
+ */
uint64_t (*get_min_page_size)(IOMMUMemoryRegion *iommu);
- /* Called when IOMMU Notifier flag changed */
+ /* Called when IOMMU Notifier flag changes (ie when the set of
+ * events which IOMMU users are requesting notification for changes).
+ * Optional method -- need not be provided if the IOMMU does not
+ * need to know exactly which events must be notified.
+ *
+ * @iommu: the IOMMUMemoryRegion
+ * @old_flags: events which previously needed to be notified
+ * @new_flags: events which now need to be notified
+ */
void (*notify_flag_changed)(IOMMUMemoryRegion *iommu,
IOMMUNotifierFlag old_flags,
IOMMUNotifierFlag new_flags);
- /* Set this up to provide customized IOMMU replay function */
+ /* Called to handle memory_region_iommu_replay().
+ *
+ * The default implementation of memory_region_iommu_replay() is to
+ * call the IOMMU translate method for every page in the address space
+ * with flag == IOMMU_NONE and then call the notifier if translate
+ * returns a valid mapping. If this method is implemented then it
+ * overrides the default behaviour, and must provide the full semantics
+ * of memory_region_iommu_replay(), by calling @notifier for every
+ * translation present in the IOMMU.
+ *
+ * Optional method -- an IOMMU only needs to provide this method
+ * if the default is inefficient or produces undesirable side effects.
+ *
+ * Note: this is not related to record-and-replay functionality.
+ */
void (*replay)(IOMMUMemoryRegion *iommu, IOMMUNotifier *notifier);
- /* Get IOMMU misc attributes */
- int (*get_attr)(IOMMUMemoryRegion *iommu, enum IOMMUMemoryRegionAttr,
+ /* Get IOMMU misc attributes. This is an optional method that
+ * can be used to allow users of the IOMMU to get implementation-specific
+ * information. The IOMMU implements this method to handle calls
+ * by IOMMU users to memory_region_iommu_get_attr() by filling in
+ * the arbitrary data pointer for any IOMMUMemoryRegionAttr values that
+ * the IOMMU supports. If the method is unimplemented then
+ * memory_region_iommu_get_attr() will always return -EINVAL.
+ *
+ * @iommu: the IOMMUMemoryRegion
+ * @attr: attribute being queried
+ * @data: memory to fill in with the attribute data
+ *
+ * Returns 0 on success, or a negative errno; in particular
+ * returns -EINVAL for unrecognized or unimplemented attribute types.
+ */
+ int (*get_attr)(IOMMUMemoryRegion *iommu, enum IOMMUMemoryRegionAttr attr,
void *data);
} IOMMUMemoryRegionClass;
@@ -705,6 +776,14 @@ static inline void
memory_region_init_reservation(MemoryRegion *mr,
* An IOMMU region translates addresses and forwards accesses to a target
* memory region.
*
+ * The IOMMU implementation must define a subclass of TYPE_IOMMU_MEMORY_REGION.
+ * @_iommu_mr should be a pointer to enough memory for an instance of
+ * that subclass, @instance_size is the size of that subclass, and
+ * @mrtypename is its name. This function will initialize @_iommu_mr as an
+ * instance of the subclass, and its methods will then be called to handle
+ * accesses to the memory region. See the documentation of
+ * #IOMMUMemoryRegionClass for further details.
+ *
* @_iommu_mr: the #IOMMUMemoryRegion to be initialized
* @instance_size: the IOMMUMemoryRegion subclass instance size
* @mrtypename: the type name of the #IOMMUMemoryRegion
@@ -953,6 +1032,8 @@ void memory_region_register_iommu_notifier(MemoryRegion
*mr,
* a notifier with the minimum page granularity returned by
* mr->iommu_ops->get_page_size().
*
+ * Note: this is not related to record-and-replay functionality.
+ *
* @iommu_mr: the memory region to observe
* @n: the notifier to which to replay iommu mappings
*/
@@ -962,6 +1043,8 @@ void memory_region_iommu_replay(IOMMUMemoryRegion
*iommu_mr, IOMMUNotifier *n);
* memory_region_iommu_replay_all: replay existing IOMMU translations
* to all the notifiers registered.
*
+ * Note: this is not related to record-and-replay functionality.
+ *
* @iommu_mr: the memory region to observe
*/
void memory_region_iommu_replay_all(IOMMUMemoryRegion *iommu_mr);
@@ -981,7 +1064,9 @@ void memory_region_unregister_iommu_notifier(MemoryRegion
*mr,
* memory_region_iommu_get_attr: return an IOMMU attr if get_attr() is
* defined on the IOMMU.
*
- * Returns 0 if succeded, error code otherwise.
+ * Returns 0 on success, or a negative errno otherwise. In particular,
+ * -EINVAL indicates that the IOMMU does not support the requested
+ * attribute.
*
* @iommu_mr: the memory region
* @attr: the requested attribute
--
2.17.0
