[PATCH 05/40] dma-contiguous: add dma_get_numa_cma_area() accessor

[Alexander Graf <graf@amazon.com>]

With Nitro Sandboxes, we want to allocate per-NUMA memory from the DMA
contiguous allocator, but have no per-NUMA struct device to pass in.
dma_alloc_contiguous() takes the node from dev_to_node(dev), and the
per-node areas sit in dma_contiguous_numa_area[], which is static.

So instead, introduce dma_get_numa_cma_area(), which returns the generic
per-NUMA DMA CMA area that cma_alloc() would use. This way, the
nitro_enclaves driver can build its own generic CMA pool per-node
allocation logic on top of those pools.

Signed-off-by: Alexander Graf <graf@amazon.com>
---
 include/linux/dma-map-ops.h |  7 +++++++
 kernel/dma/contiguous.c     | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
index afaf2c12189b8..5f7138ea6899a 100644
--- a/include/linux/dma-map-ops.h
+++ b/include/linux/dma-map-ops.h
@@ -93,6 +93,7 @@ static inline void set_dma_ops(struct device *dev,
 #ifdef CONFIG_DMA_CMA
 struct cma *dev_get_cma_area(struct device *dev);
 struct cma *dma_contiguous_get_area_by_idx(unsigned int idx);
+struct cma *dma_get_numa_cma_area(int nid);
 
 void dma_contiguous_reserve(phys_addr_t addr_limit);
 int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
@@ -115,6 +116,12 @@ static inline struct cma *dma_contiguous_get_area_by_idx(unsigned int idx)
 {
 	return NULL;
 }
+
+static inline struct cma *dma_get_numa_cma_area(int nid)
+{
+	return NULL;
+}
+
 static inline void dma_contiguous_reserve(phys_addr_t limit)
 {
 }
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 90937dc7c627d..363b84284d087 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -443,6 +443,42 @@ struct page *dma_alloc_contiguous(struct device *dev, size_t size, gfp_t gfp)
 	return cma_alloc_aligned(dma_contiguous_default_area, size, gfp);
 }
 
+/**
+ * dma_get_numa_cma_area() - get the CMA area a NUMA node can allocate from
+ * @nid: NUMA node id
+ *
+ * dma_alloc_contiguous() picks a per-node CMA area from dev_to_node(dev),
+ * which a caller cannot override on a per-request basis. This accessor
+ * returns the area a specific node can allocate from, so a caller can
+ * cma_alloc() from the node it wants.
+ *
+ * A per-node area comes from numa_cma= or cma_pernuma=, or from
+ * CONFIG_CMA_SIZE_PERNUMA, which reserves the default area's size on every
+ * online node on top of the default area itself, all three of which are
+ * CONFIG_DMA_NUMA_CMA. Where there is one online node this returns the default
+ * area, so a host that reserved only cma= reaches its reservation through this
+ * accessor as well, and that holds however CONFIG_DMA_NUMA_CMA is set.
+ *
+ * Return: the area @nid can allocate from, or NULL if @nid has none or is not
+ * a valid node (including NUMA_NO_NODE).
+ */
+struct cma *dma_get_numa_cma_area(int nid)
+{
+	if ((unsigned int)nid >= MAX_NUMNODES)
+		return NULL;
+
+#ifdef CONFIG_DMA_NUMA_CMA
+	if (dma_contiguous_numa_area[nid])
+		return dma_contiguous_numa_area[nid];
+#endif
+
+	if (nr_online_nodes == 1 && node_online(nid))
+		return dma_contiguous_default_area;
+
+	return NULL;
+}
+EXPORT_SYMBOL_GPL(dma_get_numa_cma_area);
+
 /**
  * dma_free_contiguous() - release allocated pages
  * @dev:   Pointer to device for which the pages were allocated.
-- 
2.47.1