Re: [PATCH v4 0/2] Support zero-sized HDM decoders

["Dan Williams (nvidia)" <djbw@kernel.org>]

Dan Williams (nvidia) wrote:
[..]
> I think the way to solve this is something like below (untested).

...whoops and unset apparently.

> It keeps @hdm_end aligned with the available decoders, and tracks the
> start of zero allocations relative to their skip. I believe it may
> also address the Sashiko report.

-- >8 --
diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
index 0c80b76a5f9b..3f9d97c9a3b7 100644
--- a/drivers/cxl/core/hdm.c
+++ b/drivers/cxl/core/hdm.c
@@ -209,6 +209,14 @@ void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds)
 }
 EXPORT_SYMBOL_NS_GPL(cxl_dpa_debug, "CXL");
 
+static void cxl_dpa_release_region(struct resource *parent, struct resource *res)
+{
+	/* zero sized decoders are not tracked in tree */
+	if (resource_size(res) == 0)
+		kfree(res);
+	__release_region(parent, res->start, resource_size(res));
+}
+
 /* See request_skip() kernel-doc */
 static resource_size_t __adjust_skip(struct cxl_dev_state *cxlds,
 				     const resource_size_t skip_base,
@@ -256,7 +264,7 @@ static void __cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
 
 	/* save @skip_start, before @res is released */
 	skip_start = res->start - cxled->skip;
-	__release_region(&cxlds->dpa_res, res->start, resource_size(res));
+	cxl_dpa_release_region(&cxlds->dpa_res, res);
 	if (cxled->skip)
 		release_skip(cxlds, skip_start, cxled->skip);
 	cxled->skip = 0;
@@ -336,6 +344,22 @@ static int request_skip(struct cxl_dev_state *cxlds,
 	return -EBUSY;
 }
 
+static struct resource *cxl_dpa_request_region(struct resource *parent,
+					       resource_size_t start,
+					       resource_size_t n,
+					       const char *name)
+{
+	if (!n) {
+		struct resource *res = kmalloc_obj(*res);
+
+		if (!res)
+			return NULL;
+		*res = DEFINE_RES_NAMED(start, n, name, 0);
+		return res;
+	}
+	return __request_region(parent, start, n, name, 0);
+}
+
 static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 			     resource_size_t base, resource_size_t len,
 			     resource_size_t skipped)
@@ -349,12 +373,6 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 
 	lockdep_assert_held_write(&cxl_rwsem.dpa);
 
-	if (!len) {
-		dev_warn(dev, "decoder%d.%d: empty reservation attempted\n",
-			 port->id, cxled->cxld.id);
-		return -EINVAL;
-	}
-
 	if (cxled->dpa_res) {
 		dev_dbg(dev, "decoder%d.%d: existing allocation %pr assigned\n",
 			port->id, cxled->cxld.id, cxled->dpa_res);
@@ -378,8 +396,8 @@ static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
 		if (rc)
 			return rc;
 	}
-	res = __request_region(&cxlds->dpa_res, base, len,
-			       dev_name(&cxled->cxld.dev), 0);
+	res = cxl_dpa_request_region(&cxlds->dpa_res, base, len,
+				     dev_name(&cxled->cxld.dev));
 	if (!res) {
 		dev_dbg(dev, "decoder%d.%d: failed to reserve allocation\n",
 			port->id, cxled->cxld.id);
@@ -545,7 +563,7 @@ int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
 	struct device *dev = &cxled->cxld.dev;
 
 	guard(rwsem_write)(&cxl_rwsem.dpa);
-	if (!cxled->dpa_res)
+	if (!cxled->dpa_res || !resource_size(cxled->dpa_res))
 		return 0;
 	if (cxled->cxld.region) {
 		dev_dbg(dev, "decoder assigned to: %s\n",
diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index 7c6c5b7450a5..6f4d634b2cfb 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -1433,6 +1433,9 @@ int cxl_mem_get_poison(struct cxl_memdev *cxlmd, u64 offset, u64 len,
 	int nr_records = 0;
 	int rc;
 
+	if (!len)
+		return 0;
+
 	ACQUIRE(mutex_intr, lock)(&mds->poison.mutex);
 	if ((rc = ACQUIRE_ERR(mutex_intr, &lock)))
 		return rc;
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
index e50dc716d4e8..0d03e3bedb40 100644
--- a/drivers/cxl/core/region.c
+++ b/drivers/cxl/core/region.c
@@ -2090,7 +2090,7 @@ static int cxl_region_attach(struct cxl_region *cxlr,
 		return -ENXIO;
 	}
 
-	if (!cxled->dpa_res) {
+	if (!cxled->dpa_res || !resource_size(cxled->dpa_res)) {
 		dev_dbg(&cxlr->dev, "%s:%s: missing DPA allocation.\n",
 			dev_name(&cxlmd->dev), dev_name(&cxled->cxld.dev));
 		return -ENXIO;