[PATCH] x86/mm: Print the encryption features correctly when a paravisor is present

[Dexuan Cui]

Hyper-V provides two modes for running a TDX/SNP VM:

1) In TD Partitioning mode (TDX) or vTOM mode (SNP) with a paravisor;
2) In "fully enlightened" mode with the normal TDX shared bit or SNP C-bit
   control over page encryption, and no paravisor.

In the first mode (i.e. paravisor mode), the native TDX/SNP CPUID
capability is hidden from the VM, but cc_platform_has(CC_ATTR_MEM_ENCRYPT)
and cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT) are true; as a result,
mem_encrypt_init() incorrectly prints the below message when an Intel TDX
VM with a paravisor runs on Hyper-V:
"Memory Encryption Features active: AMD SEV".

Introduce x86_platform.print_mem_enc_feature_info and allow hv_vtom_init()
to override the function pointer so that the correct message is printed.

BTW, when a VBS (Virtualization-based Security) VM running on Hyper-V
(the physical CPU can be an AMD CPU or an Intel CPU), the VM's memory is
not encrypted, but mem_encrypt_init() also prints the same incorrect
message. The introduction of x86_platform.print_mem_enc_feature_info can
also fix the issue.

Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
---

Some open questions:

1. Should we refactor the existing print_memory_encrypt_feature_info()
into a TDX-specific function and an SEV-specific function?  The
function pointer in x86_platform_ops would be initialized to a no-op
function, and then early_tdx_init(), sme_enable() and hv_vtom_init()
would fill it in accordingly.

2. Should we rename "print_mem_enc_feature_info()" to
"print_coco_feature_info()"?  CC_ATTR_GUEST_STATE_ENCRYPT (and
CC_ATTR_GUEST_SEV_SNP?) may not look like *memory* encryption to me?

 arch/x86/hyperv/ivm.c              | 11 +++++++++++
 arch/x86/include/asm/mem_encrypt.h |  1 +
 arch/x86/include/asm/x86_init.h    |  2 ++
 arch/x86/kernel/x86_init.c         |  1 +
 arch/x86/mm/mem_encrypt.c          |  4 ++--
 5 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index e68051eba25a..fdc2fab0415e 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -450,6 +450,16 @@ static bool hv_is_private_mmio(u64 addr)
 	return false;
 }
 
+static void hv_print_mem_enc_feature_info(void)
+{
+	enum hv_isolation_type type = hv_get_isolation_type();
+
+	if (type == HV_ISOLATION_TYPE_SNP)
+		pr_info("Memory Encryption Features active: AMD SEV\n");
+	else if (type == HV_ISOLATION_TYPE_TDX)
+		pr_info("Memory Encryption Features active: Intel TDX\n");
+}
+
 void __init hv_vtom_init(void)
 {
 	enum hv_isolation_type type = hv_get_isolation_type();
@@ -479,6 +489,7 @@ void __init hv_vtom_init(void)
 	cc_set_mask(ms_hyperv.shared_gpa_boundary);
 	physical_mask &= ms_hyperv.shared_gpa_boundary - 1;
 
+	x86_platform.print_mem_enc_feature_info = hv_print_mem_enc_feature_info;
 	x86_platform.hyper.is_private_mmio = hv_is_private_mmio;
 	x86_platform.guest.enc_cache_flush_required = hv_vtom_cache_flush_required;
 	x86_platform.guest.enc_tlb_flush_required = hv_vtom_tlb_flush_required;
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index 7f97a8a97e24..6e8050a9138e 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -19,6 +19,7 @@
 
 #ifdef CONFIG_X86_MEM_ENCRYPT
 void __init mem_encrypt_init(void);
+void print_mem_encrypt_feature_info(void);
 #else
 static inline void mem_encrypt_init(void) { }
 #endif
diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 14b0562c1d8b..7798174d4b8d 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -291,6 +291,7 @@ struct x86_hyper_runtime {
  * 				semantics.
  * @realmode_reserve:		reserve memory for realmode trampoline
  * @realmode_init:		initialize realmode trampoline
+ * @print_mem_enc_feature_info:	print the supported memory encryption features
  * @hyper:			x86 hypervisor specific runtime callbacks
  */
 struct x86_platform_ops {
@@ -309,6 +310,7 @@ struct x86_platform_ops {
 	void (*set_legacy_features)(void);
 	void (*realmode_reserve)(void);
 	void (*realmode_init)(void);
+	void (*print_mem_enc_feature_info)(void);
 	struct x86_hyper_runtime hyper;
 	struct x86_guest guest;
 };
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index 6117662ae4e6..ccb53db1b51e 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -149,6 +149,7 @@ struct x86_platform_ops x86_platform __ro_after_init = {
 	.restore_sched_clock_state	= tsc_restore_sched_clock_state,
 	.realmode_reserve		= reserve_real_mode,
 	.realmode_init			= init_real_mode,
+	.print_mem_enc_feature_info	= print_mem_encrypt_feature_info,
 	.hyper.pin_vcpu			= x86_op_int_noop,
 	.hyper.is_private_mmio		= is_private_mmio_noop,
 
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 9f27e14e185f..8d37048bc1df 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -39,7 +39,7 @@ bool force_dma_unencrypted(struct device *dev)
 	return false;
 }
 
-static void print_mem_encrypt_feature_info(void)
+void print_mem_encrypt_feature_info(void)
 {
 	pr_info("Memory Encryption Features active:");
 
@@ -84,5 +84,5 @@ void __init mem_encrypt_init(void)
 	/* Call into SWIOTLB to update the SWIOTLB DMA buffers */
 	swiotlb_update_mem_attributes();
 
-	print_mem_encrypt_feature_info();
+	x86_platform.print_mem_enc_feature_info();
 }
-- 
2.25.1