[RFC PATCH 09/14] arm64: Enforce bounce buffers for realm DMA

Steven Price
2023-01-27T11:30:43Z

Within a realm guest it's not possible for a device emulated by the VMM
to access arbitrary guest memory. So force the use of bounce buffers to
ensure that the memory the emulated devices are accessing is in memory
which is explicitly shared with the host.

Co-developed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
---
arch/arm64/kernel/rsi.c | 2 ++
arch/arm64/mm/init.c | 8 +++++++-
2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 49d36dfe0064..1a07eefdd2e9 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -5,6 +5,8 @@

#include <linux/jump_label.h>
#include <linux/memblock.h>
+#include <linux/swiotlb.h>
+
#include <asm/rsi.h>

struct realm_config __attribute((aligned(PAGE_SIZE))) config;
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index fa9088add624..32a4710ad861 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -472,7 +472,13 @@ void __init bootmem_init(void)
*/
void __init mem_init(void)
{
- swiotlb_init(max_pfn > PFN_DOWN(arm64_dma_phys_limit), SWIOTLB_VERBOSE);
+ if (is_realm_world()) {
+ swiotlb_init(true, SWIOTLB_VERBOSE | SWIOTLB_FORCE);
+ swiotlb_update_mem_attributes();
+ } else {
+ swiotlb_init(max_pfn > PFN_DOWN(arm64_dma_phys_limit),
+ SWIOTLB_VERBOSE);
+ }

/* this will put all unused low memory onto the freelists */
memblock_free_all();
--
2.34.1