[PATCH v5 06/10] swiotlb: Reject misaligned restricted DMA pools for CoCo guests

[Aneesh Kumar K.V (Arm)]

Restricted DMA pools are described by firmware reserved-memory nodes and
are not resized or realigned by the kernel. For confidential-computing
guests, such pools can only be shared safely when both the base address and
size are aligned to the shared-granule size.

Reject restricted DMA pools that are not aligned to
mem_cc_shared_granule_size() when guest memory encryption is active.

Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar at kernel.org>
---
 kernel/dma/swiotlb.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
index 1d77746b6f31..ad8a1ccf3977 100644
--- a/kernel/dma/swiotlb.c
+++ b/kernel/dma/swiotlb.c
@@ -2002,6 +2002,20 @@ static int rmem_swiotlb_device_init(struct reserved_mem *rmem,
 		 * if platform supports memory encryption,
 		 * restricted mem pool is shared by default
 		 */
+		if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
+			size_t cc_shared_granule_size = mem_cc_shared_granule_size();
+
+			if (!IS_ALIGNED(rmem->base, cc_shared_granule_size) ||
+			    !IS_ALIGNED(rmem->size, cc_shared_granule_size)) {
+				dev_err(dev, "Restricted DMA pool must be aligned to %#zx bytes for memory encryption\n",
+					cc_shared_granule_size);
+				kfree(pool->areas);
+				kfree(pool->slots);
+				kfree(mem);
+				return -EINVAL;
+			}
+		}
+
 		if (cc_platform_has(CC_ATTR_MEM_ENCRYPT)) {
 			int ret;
 
-- 
2.43.0