[PATCH v4 07/15] arm64: Enforce bounce buffers for realm DMA

Steven Price
2024-07-01T09:55:41Z

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.

This adds a call to swiotlb_update_mem_attributes() which calls
set_memory_decrypted() to ensure the bounce buffer memory is shared with
the host. For non-realm guests or hosts this is a no-op.

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>
---
v3: Simplify mem_init() by using a 'flags' variable.
---
arch/arm64/kernel/rsi.c | 2 ++
arch/arm64/mm/init.c | 10 +++++++++-
2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 7ac5fc4a27d0..918db258cd4a 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -6,6 +6,8 @@
#include <linux/jump_label.h>
#include <linux/memblock.h>
#include <linux/psci.h>
+#include <linux/swiotlb.h>
+
#include <asm/rsi.h>

struct realm_config config;
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 9b5ab6818f7f..1d595b63da71 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -41,6 +41,7 @@
#include <asm/kvm_host.h>
#include <asm/memory.h>
#include <asm/numa.h>
+#include <asm/rsi.h>
#include <asm/sections.h>
#include <asm/setup.h>
#include <linux/sizes.h>
@@ -369,8 +370,14 @@ void __init bootmem_init(void)
*/
void __init mem_init(void)
{
+ unsigned int flags = SWIOTLB_VERBOSE;
bool swiotlb = max_pfn > PFN_DOWN(arm64_dma_phys_limit);

+ if (is_realm_world()) {
+ swiotlb = true;
+ flags |= SWIOTLB_FORCE;
+ }
+
if (IS_ENABLED(CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC) && !swiotlb) {
/*
* If no bouncing needed for ZONE_DMA, reduce the swiotlb
@@ -382,7 +389,8 @@ void __init mem_init(void)
swiotlb = true;
}

- swiotlb_init(swiotlb, SWIOTLB_VERBOSE);
+ swiotlb_init(swiotlb, flags);
+ swiotlb_update_mem_attributes();

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