From fbf979a01375704fa87c559763209c658593b6f8 Mon Sep 17 00:00:00 2001
From: Steven Price <steven.price@arm.com>
Date: Thu, 17 Oct 2024 14:14:30 +0100
Subject: [PATCH] arm64: Enforce bounce buffers for realm DMA

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.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
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>
Link: https://lore.kernel.org/r/20241017131434.40935-8-steven.price@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
 arch/arm64/kernel/rsi.c |  1 +
 arch/arm64/mm/init.c    | 10 +++++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 3e0c83e2296f5..a23c0a7154d2a 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -6,6 +6,7 @@
 #include <linux/jump_label.h>
 #include <linux/memblock.h>
 #include <linux/psci.h>
+#include <linux/swiotlb.h>
 
 #include <asm/io.h>
 #include <asm/rsi.h>
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index 27a32ff15412a..d21f67d67cf5f 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>
@@ -366,8 +367,14 @@ 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
@@ -379,7 +386,8 @@ 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();