[RFC PATCH 5/7] mm/damon: add sysfs binding and dispatch hookup for paddr_ibs operations

[Ravi Jonnalagadda <ravis.opensrc@gmail.com>]

Extend damon_ops_id enum to include DAMON_OPS_PADDR_IBS and add the
corresponding 'paddr_ibs' name to the sysfs ops_names array so users
can select AMD IBS-based PA-mode monitoring via
/sys/kernel/mm/damon/admin/kdamonds/<N>/contexts/<N>/operations.

Route ops that report accesses through the hardware-sampling ring
(currently only DAMON_OPS_PADDR_IBS) through the existing
kdamond_check_reported_accesses() drain path used for page-fault
reports.  A small helper damon_ops_is_hw_hotness() centralises the
classification so any future paddr-family backend that also reports
through the ring just adds a case here.

This routing is bound to ops.id rather than to a separate per-context
flag.  A flag in damon_sample_control would have to be set by the ops
.init callback after damon_select_ops() and would then need to be
preserved by damon_commit_sample_control() across sysfs commits;
deriving from ops.id avoids both pitfalls.

Signed-off-by: Ravi Jonnalagadda <ravis.opensrc@gmail.com>
---
 include/linux/damon.h |  2 ++
 mm/damon/core.c       | 13 ++++++++++++-
 mm/damon/sysfs.c      | 12 +++++++++---
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/include/linux/damon.h b/include/linux/damon.h
index 35cc3d42fcba8..16da528845d03 100644
--- a/include/linux/damon.h
+++ b/include/linux/damon.h
@@ -669,12 +669,14 @@ struct damos {
  * @DAMON_OPS_FVADDR:	Monitoring operations for only fixed ranges of virtual
  *			address spaces
  * @DAMON_OPS_PADDR:	Monitoring operations for the physical address space
+ * @DAMON_OPS_PADDR_IBS:	AMD IBS-based PA-mode monitoring
  * @NR_DAMON_OPS:	Number of monitoring operations implementations
  */
 enum damon_ops_id {
 	DAMON_OPS_VADDR,
 	DAMON_OPS_FVADDR,
 	DAMON_OPS_PADDR,
+	DAMON_OPS_PADDR_IBS,
 	NR_DAMON_OPS,
 };
 
diff --git a/mm/damon/core.c b/mm/damon/core.c
index 03f9c671e8bc9..2aa031cbc70b7 100644
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -73,6 +73,16 @@ static bool __damon_is_registered_ops(enum damon_ops_id id)
 	return true;
 }
 
+/*
+ * Returns true if the given ops id reports access samples through the
+ * hardware-sampling ring-buffer drain path (rather than its own
+ * .check_accesses callback).
+ */
+static bool damon_ops_is_hw_hotness(enum damon_ops_id id)
+{
+	return id == DAMON_OPS_PADDR_IBS;
+}
+
 /**
  * damon_is_registered_ops() - Check if a given damon_operations is registered.
  * @id:	Id of the damon_operations to check if registered.
@@ -4048,7 +4058,8 @@ static int kdamond_fn(void *data)
 		ctx->passed_sample_intervals++;
 
 		/* todo: make these non-exclusive */
-		if (ctx->sample_control.primitives_enabled.page_fault)
+		if (ctx->sample_control.primitives_enabled.page_fault ||
+		    damon_ops_is_hw_hotness(ctx->ops.id))
 			max_nr_accesses = kdamond_check_reported_accesses(ctx);
 		else if (ctx->ops.check_accesses)
 			max_nr_accesses = ctx->ops.check_accesses(ctx);
diff --git a/mm/damon/sysfs.c b/mm/damon/sysfs.c
index fc7256e522a69..261ccf0c61846 100644
--- a/mm/damon/sysfs.c
+++ b/mm/damon/sysfs.c
@@ -1388,6 +1388,10 @@ static const struct damon_sysfs_ops_name damon_sysfs_ops_names[] = {
 		.ops_id = DAMON_OPS_PADDR,
 		.name = "paddr",
 	},
+	{
+		.ops_id = DAMON_OPS_PADDR_IBS,
+		.name = "paddr_ibs",
+	},
 };
 
 struct damon_sysfs_context {
@@ -2023,7 +2027,8 @@ static int damon_sysfs_add_targets(struct damon_ctx *ctx,
 	int i, err;
 
 	/* Multiple physical address space monitoring targets makes no sense */
-	if (ctx->ops.id == DAMON_OPS_PADDR && sysfs_targets->nr > 1)
+	if ((ctx->ops.id == DAMON_OPS_PADDR ||
+	     ctx->ops.id == DAMON_OPS_PADDR_IBS) && sysfs_targets->nr > 1)
 		return -EINVAL;
 
 	for (i = 0; i < sysfs_targets->nr; i++) {
@@ -2072,8 +2077,9 @@ static int damon_sysfs_apply_inputs(struct damon_ctx *ctx,
 	if (err)
 		return err;
 	ctx->addr_unit = sys_ctx->addr_unit;
-	/* addr_unit is respected by only DAMON_OPS_PADDR */
-	if (sys_ctx->ops_id == DAMON_OPS_PADDR)
+	/* addr_unit is respected by only paddr-family ops */
+	if (sys_ctx->ops_id == DAMON_OPS_PADDR ||
+	    sys_ctx->ops_id == DAMON_OPS_PADDR_IBS)
 		ctx->min_region_sz = max(
 				DAMON_MIN_REGION_SZ / sys_ctx->addr_unit, 1);
 	ctx->pause = sys_ctx->pause;
-- 
2.43.0