[PATCH 3/3] arm64/coco: Add pKVM as a CC platform

[Mostafa Saleh]

pKVM does support memory encryption, expose that to the rest of
the kernel through cc_platform_has()

At the moment, all devices inside the guest are emulated which
requires its memory to be shared back to the host (decrypted), so
set force_dma_unencrypted() to always return true.

Although, typically pKVM guests rely on restricted-dma-pools to
bounce traffic, with this change, it is possible to solely rely on
the default SWIOTLB for that (assuming the appropriate size is set
from the command line)

Signed-off-by: Mostafa Saleh <smostafa at google.com>
---
This change is critical for the ongoing refactoring of the DMA-API[1]
that will break protected guests under pKVM with this patch. That is
due to this rework will make the state of the SWIOTLB and restricted
dma pools depends on the value returned by cc_platform_has()

[1] https://lore.kernel.org/all/20260522042815.370873-1-aneesh.kumar@kernel.org/
---
 arch/arm64/include/asm/hypervisor.h           | 13 +++++++++++++
 arch/arm64/include/asm/mem_encrypt.h          |  3 ++-
 arch/arm64/kernel/rsi.c                       | 12 ------------
 arch/arm64/mm/init.c                          | 15 ++++++++++++++-
 drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c |  3 +++
 5 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/arch/arm64/include/asm/hypervisor.h b/arch/arm64/include/asm/hypervisor.h
index a12fd897c877..8889a0ba1ec5 100644
--- a/arch/arm64/include/asm/hypervisor.h
+++ b/arch/arm64/include/asm/hypervisor.h
@@ -3,6 +3,9 @@
 #define _ASM_ARM64_HYPERVISOR_H
 
 #include <asm/xen/hypervisor.h>
+#include <linux/jump_label.h>
+
+DECLARE_STATIC_KEY_FALSE(pkvm_guest);
 
 void kvm_init_hyp_services(void);
 bool kvm_arm_hyp_service_available(u32 func_id);
@@ -10,8 +13,18 @@ void kvm_arm_target_impl_cpu_init(void);
 
 #ifdef CONFIG_ARM_PKVM_GUEST
 void pkvm_init_hyp_services(void);
+
+static inline bool is_protected_kvm_guest(void)
+{
+	return static_branch_unlikely(&pkvm_guest);
+}
 #else
 static inline void pkvm_init_hyp_services(void) { };
+
+static inline bool is_protected_kvm_guest(void)
+{
+	return false;
+}
 #endif
 
 static inline void kvm_arch_init_hyp_services(void)
diff --git a/arch/arm64/include/asm/mem_encrypt.h b/arch/arm64/include/asm/mem_encrypt.h
index 314b2b52025f..636f45b4d8af 100644
--- a/arch/arm64/include/asm/mem_encrypt.h
+++ b/arch/arm64/include/asm/mem_encrypt.h
@@ -2,6 +2,7 @@
 #ifndef __ASM_MEM_ENCRYPT_H
 #define __ASM_MEM_ENCRYPT_H
 
+#include <asm/hypervisor.h>
 #include <asm/rsi.h>
 
 struct device;
@@ -20,7 +21,7 @@ int realm_register_memory_enc_ops(void);
 
 static inline bool force_dma_unencrypted(struct device *dev)
 {
-	return is_realm_world();
+	return is_realm_world() || is_protected_kvm_guest();
 }
 
 /*
diff --git a/arch/arm64/kernel/rsi.c b/arch/arm64/kernel/rsi.c
index 92160f2e57ff..25ca75ce1a4d 100644
--- a/arch/arm64/kernel/rsi.c
+++ b/arch/arm64/kernel/rsi.c
@@ -7,7 +7,6 @@
 #include <linux/memblock.h>
 #include <linux/psci.h>
 #include <linux/swiotlb.h>
-#include <linux/cc_platform.h>
 #include <linux/platform_device.h>
 
 #include <asm/io.h>
@@ -23,17 +22,6 @@ EXPORT_SYMBOL(prot_ns_shared);
 DEFINE_STATIC_KEY_FALSE_RO(rsi_present);
 EXPORT_SYMBOL(rsi_present);
 
-bool cc_platform_has(enum cc_attr attr)
-{
-	switch (attr) {
-	case CC_ATTR_MEM_ENCRYPT:
-		return is_realm_world();
-	default:
-		return false;
-	}
-}
-EXPORT_SYMBOL_GPL(cc_platform_has);
-
 static bool rsi_version_matches(void)
 {
 	unsigned long ver_lower, ver_higher;
diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
index fcc9c05a8fe6..edcc305ec883 100644
--- a/arch/arm64/mm/init.c
+++ b/arch/arm64/mm/init.c
@@ -11,6 +11,7 @@
 #include <linux/errno.h>
 #include <linux/swap.h>
 #include <linux/init.h>
+#include <linux/cc_platform.h>
 #include <linux/cache.h>
 #include <linux/mman.h>
 #include <linux/nodemask.h>
@@ -36,6 +37,7 @@
 
 #include <asm/boot.h>
 #include <asm/fixmap.h>
+#include <asm/hypervisor.h>
 #include <asm/kasan.h>
 #include <asm/kernel-pgtable.h>
 #include <asm/kvm_host.h>
@@ -338,7 +340,7 @@ void __init arch_mm_preinit(void)
 	unsigned int flags = SWIOTLB_VERBOSE;
 	bool limited_addressing = max_pfn > PFN_DOWN(arm64_dma_phys_limit);
 
-	if (is_realm_world()) {
+	if (is_realm_world() || is_protected_kvm_guest()) {
 		flags |= SWIOTLB_FORCE;
 	} else if (!limited_addressing) {
 		/*
@@ -413,6 +415,17 @@ void dump_mem_limit(void)
 	}
 }
 
+bool cc_platform_has(enum cc_attr attr)
+{
+	switch (attr) {
+	case CC_ATTR_MEM_ENCRYPT:
+		return is_realm_world() || is_protected_kvm_guest();
+	default:
+		return false;
+	}
+}
+EXPORT_SYMBOL_GPL(cc_platform_has);
+
 #ifdef CONFIG_EXECMEM
 static u64 module_direct_base __ro_after_init = 0;
 static u64 module_plt_base __ro_after_init = 0;
diff --git a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
index d66291def0f4..26fe9c3f22e3 100644
--- a/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
+++ b/drivers/virt/coco/pkvm-guest/arm-pkvm-guest.c
@@ -17,6 +17,7 @@
 #include <asm/hypervisor.h>
 
 static size_t pkvm_granule;
+DEFINE_STATIC_KEY_FALSE_RO(pkvm_guest);
 
 static int arm_smccc_do_one_page(u32 func_id, phys_addr_t phys)
 {
@@ -120,4 +121,6 @@ void pkvm_init_hyp_services(void)
 
 	if (kvm_arm_hyp_service_available(ARM_SMCCC_KVM_FUNC_MMIO_GUARD))
 		arm64_ioremap_prot_hook_register(&mmio_guard_ioremap_hook);
+
+	static_branch_enable(&pkvm_guest);
 }
-- 
2.54.0.1032.g2f8565e1d1-goog