[PATCH v3 2/2] dma-pool: Only allocate from CMA when in same memory zone

[Nicolas Saenz Julienne]

There is no guarantee to CMA's placement, so allocating a zone specific
atomic pool from CMA might return memory from a completely different
memory zone. To get around this double check CMA's placement before
allocating from it.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulie...@suse.de>
[hch: rebased, added a fallback to the page allocator, allow dipping into
      lower CMA pools]
Signed-off-by: Christoph Hellwig <h...@lst.de>
---

Changes since v2:
 - Go back to v1 behavior

 kernel/dma/pool.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 5d071d4a3cba..30d28d761490 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -3,7 +3,9 @@
  * Copyright (C) 2012 ARM Ltd.
  * Copyright (C) 2020 Google LLC
  */
+#include <linux/cma.h>
 #include <linux/debugfs.h>
+#include <linux/dma-contiguous.h>
 #include <linux/dma-direct.h>
 #include <linux/dma-noncoherent.h>
 #include <linux/init.h>
@@ -55,6 +57,29 @@ static void dma_atomic_pool_size_add(gfp_t gfp, size_t size)
                pool_size_kernel += size;
 }
 
+static bool cma_in_zone(gfp_t gfp)
+{
+       unsigned long size;
+       phys_addr_t end;
+       struct cma *cma;
+
+       cma = dev_get_cma_area(NULL);
+       if (!cma)
+               return false;
+
+       size = cma_get_size(cma);
+       if (!size)
+               return false;
+
+       /* CMA can't cross zone boundaries, see cma_activate_area() */
+       end = cma_get_base(cma) - memblock_start_of_DRAM() + size - 1;
+       if (IS_ENABLED(CONFIG_ZONE_DMA) && (gfp & GFP_DMA))
+               return end <= DMA_BIT_MASK(zone_dma_bits);
+       if (IS_ENABLED(CONFIG_ZONE_DMA32) && (gfp & GFP_DMA32))
+               return end <= DMA_BIT_MASK(32);
+       return true;
+}
+
 static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
                              gfp_t gfp)
 {
@@ -68,7 +93,11 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t 
pool_size,
 
        do {
                pool_size = 1 << (PAGE_SHIFT + order);
-               page = alloc_pages(gfp, order);
+               if (cma_in_zone(gfp))
+                       page = dma_alloc_from_contiguous(NULL, 1 << order,
+                                                        order, false);
+               if (!page)
+                       page = alloc_pages(gfp, order);
        } while (!page && order-- > 0);
        if (!page)
                goto out;
-- 
2.28.0