dma-direct: atomic allocations must come from atomic coherent pools

When a device requires unencrypted memory and the context does not allow
blocking, memory must be returned from the atomic coherent pools.

This avoids the remap when CONFIG_DMA_DIRECT_REMAP is not enabled and the
config only requires CONFIG_DMA_COHERENT_POOL.  This will be used for
CONFIG_AMD_MEM_ENCRYPT in a subsequent patch.

Keep all memory in these pools unencrypted.  When set_memory_decrypted()
fails, this prohibits the memory from being added.  If adding memory to
the genpool fails, and set_memory_encrypted() subsequently fails, there
is no alternative other than leaking the memory.

Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

kernel/dma/direct.c

@@ -76,6 +76,39 @@ static bool dma_coherent_ok(struct device *dev, phys_addr_t phys, size_t size)
 			min_not_zero(dev->coherent_dma_mask, dev->bus_dma_limit);
 }
 
+/*
+ * Decrypting memory is allowed to block, so if this device requires
+ * unencrypted memory it must come from atomic pools.
+ */
+static inline bool dma_should_alloc_from_pool(struct device *dev, gfp_t gfp,
+					      unsigned long attrs)
+{
+	if (!IS_ENABLED(CONFIG_DMA_COHERENT_POOL))
+		return false;
+	if (gfpflags_allow_blocking(gfp))
+		return false;
+	if (force_dma_unencrypted(dev))
+		return true;
+	if (!IS_ENABLED(CONFIG_DMA_DIRECT_REMAP))
+		return false;
+	if (dma_alloc_need_uncached(dev, attrs))
+		return true;
+	return false;
+}
+
+static inline bool dma_should_free_from_pool(struct device *dev,
+					     unsigned long attrs)
+{
+	if (IS_ENABLED(CONFIG_DMA_COHERENT_POOL))
+		return true;
+	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
+	    !force_dma_unencrypted(dev))
+		return false;
+	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP))
+		return true;
+	return false;
+}
+
 struct page *__dma_direct_alloc_pages(struct device *dev, size_t size,
 		gfp_t gfp, unsigned long attrs)
 {
@@ -125,9 +158,7 @@ void *dma_direct_alloc_pages(struct device *dev, size_t size,
 	struct page *page;
 	void *ret;
 
-	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
-	    dma_alloc_need_uncached(dev, attrs) &&
-	    !gfpflags_allow_blocking(gfp)) {
+	if (dma_should_alloc_from_pool(dev, gfp, attrs)) {
 		ret = dma_alloc_from_pool(dev, PAGE_ALIGN(size), &page, gfp);
 		if (!ret)
 			return NULL;
@@ -204,17 +235,18 @@ void dma_direct_free_pages(struct device *dev, size_t size, void *cpu_addr,
 {
 	unsigned int page_order = get_order(size);
 
+	/* If cpu_addr is not from an atomic pool, dma_free_from_pool() fails */
+	if (dma_should_free_from_pool(dev, attrs) &&
+	    dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
+		return;
+
 	if ((attrs & DMA_ATTR_NO_KERNEL_MAPPING) &&
 	    !force_dma_unencrypted(dev)) {
 		/* cpu_addr is a struct page cookie, not a kernel address */
 		dma_free_contiguous(dev, cpu_addr, size);
 		return;
 	}
 
-	if (IS_ENABLED(CONFIG_DMA_DIRECT_REMAP) &&
-	    dma_free_from_pool(dev, cpu_addr, PAGE_ALIGN(size)))
-		return;
-
 	if (force_dma_unencrypted(dev))
 		set_memory_encrypted((unsigned long)cpu_addr, 1 << page_order);
 

kernel/dma/pool.c

@@ -8,6 +8,7 @@
 #include <linux/dma-contiguous.h>
 #include <linux/init.h>
 #include <linux/genalloc.h>
+#include <linux/set_memory.h>
 #include <linux/slab.h>
 #include <linux/workqueue.h>
 
@@ -53,22 +54,42 @@ static int atomic_pool_expand(struct gen_pool *pool, size_t pool_size,
 
 	arch_dma_prep_coherent(page, pool_size);
 
+#ifdef CONFIG_DMA_DIRECT_REMAP
 	addr = dma_common_contiguous_remap(page, pool_size,
 					   pgprot_dmacoherent(PAGE_KERNEL),
 					   __builtin_return_address(0));
 	if (!addr)
 		goto free_page;
-
+#else
+	addr = page_to_virt(page);
+#endif
+	/*
+	 * Memory in the atomic DMA pools must be unencrypted, the pools do not
+	 * shrink so no re-encryption occurs in dma_direct_free_pages().
+	 */
+	ret = set_memory_decrypted((unsigned long)page_to_virt(page),
+				   1 << order);
+	if (ret)
+		goto remove_mapping;
 	ret = gen_pool_add_virt(pool, (unsigned long)addr, page_to_phys(page),
 				pool_size, NUMA_NO_NODE);
 	if (ret)
-		goto remove_mapping;
+		goto encrypt_mapping;
 
 	return 0;
 
+encrypt_mapping:
+	ret = set_memory_encrypted((unsigned long)page_to_virt(page),
+				   1 << order);
+	if (WARN_ON_ONCE(ret)) {
+		/* Decrypt succeeded but encrypt failed, purposely leak */
+		goto out;
+	}
 remove_mapping:
+#ifdef CONFIG_DMA_DIRECT_REMAP
 	dma_common_free_remap(addr, pool_size);
-free_page:
+#endif
+free_page: __maybe_unused
 	if (!dma_release_from_contiguous(NULL, page, 1 << order))
 		__free_pages(page, order);
 out: