arm64/coco: Add pKVM as a CC platform

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@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Tested-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

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)

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();
 }
 
 /*

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;

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>
@@ -337,7 +339,7 @@ void __init arch_mm_preinit(void)
 {
 	unsigned int flags = SWIOTLB_VERBOSE;
 
-	if (is_realm_world()) {
+	if (is_realm_world() || is_protected_kvm_guest()) {
 		flags |= SWIOTLB_FORCE;
 	} else if (max_pfn <= PFN_DOWN(arm64_dma_phys_limit)) {
 		/*
@@ -412,6 +414,17 @@ 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;

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);
 }