[PATCH v15 10/12] swiotlb: Add restricted DMA pool initialization

[Claire Chang <tientzu@xxxxxxxxxxxx>]

Add the initialization function to create restricted DMA pools from
matching reserved-memory nodes.

Regardless of swiotlb setting, the restricted DMA pool is preferred if
available.

The restricted DMA pools provide a basic level of protection against the
DMA overwriting buffer contents at unexpected times. However, to protect
against general data leakage and system memory corruption, the system
needs to provide a way to lock down the memory access, e.g., MPU.

Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Tested-by: Will Deacon <will@xxxxxxxxxx>
---
 include/linux/swiotlb.h |  3 +-
 kernel/dma/Kconfig      | 14 ++++++++
 kernel/dma/swiotlb.c    | 76 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+), 1 deletion(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3b9454d1e498..39284ff2a6cd 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -73,7 +73,8 @@ extern enum swiotlb_force swiotlb_force;
  *             range check to see if the memory was in fact allocated by this
  *             API.
  * @nslabs:    The number of IO TLB blocks (in groups of 64) between @start and
- *             @end. This is command line adjustable via setup_io_tlb_npages.
+ *             @end. For default swiotlb, this is command line adjustable via
+ *             setup_io_tlb_npages.
  * @used:      The number of used IO TLB block.
  * @list:      The free list describing the number of free entries available
  *             from each index.
diff --git a/kernel/dma/Kconfig b/kernel/dma/Kconfig
index 77b405508743..3e961dc39634 100644
--- a/kernel/dma/Kconfig
+++ b/kernel/dma/Kconfig
@@ -80,6 +80,20 @@ config SWIOTLB
        bool
        select NEED_DMA_MAP_STATE
 
+config DMA_RESTRICTED_POOL
+       bool "DMA Restricted Pool"
+       depends on OF && OF_RESERVED_MEM
+       select SWIOTLB
+       help
+         This enables support for restricted DMA pools which provide a level of
+         DMA memory protection on systems with limited hardware protection
+         capabilities, such as those lacking an IOMMU.
+
+         For more information see
+         
<Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt>
+         and <kernel/dma/swiotlb.c>.
+         If unsure, say "n".
+
 #
 # Should be selected if we can mmap non-coherent mappings to userspace.
 # The only thing that is really required is a way to set an uncached bit
diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 6a7c6e30eb4b..3baf49c9b766 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -39,6 +39,13 @@
 #ifdef CONFIG_DEBUG_FS
 #include <linux/debugfs.h>
 #endif
+#ifdef CONFIG_DMA_RESTRICTED_POOL
+#include <linux/io.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+#include <linux/of_reserved_mem.h>
+#include <linux/slab.h>
+#endif
 
 #include <asm/io.h>
 #include <asm/dma.h>
@@ -737,4 +744,73 @@ bool swiotlb_free(struct device *dev, struct page *page, 
size_t size)
        return true;
 }
 
+static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
+                                   struct device *dev)
+{
+       struct io_tlb_mem *mem = rmem->priv;
+       unsigned long nslabs = rmem->size >> IO_TLB_SHIFT;
+
+       /*
+        * Since multiple devices can share the same pool, the private data,
+        * io_tlb_mem struct, will be initialized by the first device attached
+        * to it.
+        */
+       if (!mem) {
+               mem = kzalloc(struct_size(mem, slots, nslabs), GFP_KERNEL);
+               if (!mem)
+                       return -ENOMEM;
+
+               set_memory_decrypted((unsigned long)phys_to_virt(rmem->base),
+                                    rmem->size >> PAGE_SHIFT);
+               swiotlb_init_io_tlb_mem(mem, rmem->base, nslabs, false);
+               mem->force_bounce = true;
+               mem->for_alloc = true;
+
+               rmem->priv = mem;
+
+               if (IS_ENABLED(CONFIG_DEBUG_FS)) {
+                       mem->debugfs =
+                               debugfs_create_dir(rmem->name, debugfs_dir);
+                       swiotlb_create_debugfs_files(mem);
+               }
+       }
+
+       dev->dma_io_tlb_mem = mem;
+
+       return 0;
+}
+
+static void rmem_swiotlb_device_release(struct reserved_mem *rmem,
+                                       struct device *dev)
+{
+       dev->dma_io_tlb_mem = io_tlb_default_mem;
+}
+
+static const struct reserved_mem_ops rmem_swiotlb_ops = {
+       .device_init = rmem_swiotlb_device_init,
+       .device_release = rmem_swiotlb_device_release,
+};
+
+static int __init rmem_swiotlb_setup(struct reserved_mem *rmem)
+{
+       unsigned long node = rmem->fdt_node;
+
+       if (of_get_flat_dt_prop(node, "reusable", NULL) ||
+           of_get_flat_dt_prop(node, "linux,cma-default", NULL) ||
+           of_get_flat_dt_prop(node, "linux,dma-default", NULL) ||
+           of_get_flat_dt_prop(node, "no-map", NULL))
+               return -EINVAL;
+
+       if (PageHighMem(pfn_to_page(PHYS_PFN(rmem->base)))) {
+               pr_err("Restricted DMA pool must be accessible within the 
linear mapping.");
+               return -EINVAL;
+       }
+
+       rmem->ops = &rmem_swiotlb_ops;
+       pr_info("Reserved memory: created restricted DMA pool at %pa, size %ld 
MiB\n",
+               &rmem->base, (unsigned long)rmem->size / SZ_1M);
+       return 0;
+}
+
+RESERVEDMEM_OF_DECLARE(dma, "restricted-dma-pool", rmem_swiotlb_setup);
 #endif /* CONFIG_DMA_RESTRICTED_POOL */
-- 
2.32.0.288.g62a8d224e6-goog