x86/hyperv: Add hv_isolation_type_tdx() to detect TDX guests

No logic change to SNP/VBS guests.

hv_isolation_type_tdx() will be used to instruct a TDX guest on Hyper-V to
do some TDX-specific operations, e.g. for a fully enlightened TDX guest
(i.e. without the paravisor), hv_do_hypercall() should use
__tdx_hypercall() and such a guest on Hyper-V should handle the Hyper-V
Event/Message/Monitor pages specially.
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230824080712.30327-2-decui@microsoft.com

arch/x86/hyperv/ivm.c

@@ -562,3 +562,12 @@ bool hv_isolation_type_en_snp(void)
 	return static_branch_unlikely(&isolation_type_en_snp);
 }
 
+DEFINE_STATIC_KEY_FALSE(isolation_type_tdx);
+/*
+ * hv_isolation_type_tdx - Check if the system runs in an Intel TDX based
+ * isolated VM.
+ */
+bool hv_isolation_type_tdx(void)
+{
+	return static_branch_unlikely(&isolation_type_tdx);
+}

arch/x86/include/asm/hyperv-tlfs.h

@@ -169,7 +169,8 @@
 enum hv_isolation_type {
 	HV_ISOLATION_TYPE_NONE	= 0,
 	HV_ISOLATION_TYPE_VBS	= 1,
-	HV_ISOLATION_TYPE_SNP	= 2
+	HV_ISOLATION_TYPE_SNP	= 2,
+	HV_ISOLATION_TYPE_TDX	= 3
 };
 
 /* Hyper-V specific model specific registers (MSRs) */

arch/x86/include/asm/mshyperv.h

@@ -27,6 +27,7 @@ union hv_ghcb;
 
 DECLARE_STATIC_KEY_FALSE(isolation_type_snp);
 DECLARE_STATIC_KEY_FALSE(isolation_type_en_snp);
+DECLARE_STATIC_KEY_FALSE(isolation_type_tdx);
 
 typedef int (*hyperv_fill_flush_list_func)(
 		struct hv_guest_mapping_flush_list *flush,
@@ -49,6 +50,8 @@ extern u64 hv_current_partition_id;
 extern union hv_ghcb * __percpu *hv_ghcb_pg;
 
 extern bool hv_isolation_type_en_snp(void);
+bool hv_isolation_type_tdx(void);
+
 /*
  * DEFAULT INIT GPAT and SEGMENT LIMIT value in struct VMSA
  * to start AP in enlightened SEV guest.

arch/x86/kernel/cpu/mshyperv.c

@@ -418,6 +418,8 @@ static void __init ms_hyperv_init_platform(void)
 				static_branch_enable(&isolation_type_snp);
 			else
 				static_branch_enable(&isolation_type_en_snp);
+		} else if (hv_get_isolation_type() == HV_ISOLATION_TYPE_TDX) {
+			static_branch_enable(&isolation_type_tdx);
 		}
 	}
 

drivers/hv/hv_common.c

@@ -521,6 +521,12 @@ bool __weak hv_isolation_type_en_snp(void)
 }
 EXPORT_SYMBOL_GPL(hv_isolation_type_en_snp);
 
+bool __weak hv_isolation_type_tdx(void)
+{
+	return false;
+}
+EXPORT_SYMBOL_GPL(hv_isolation_type_tdx);
+
 void __weak hv_setup_vmbus_handler(void (*handler)(void))
 {
 }

include/asm-generic/mshyperv.h

@@ -66,6 +66,7 @@ extern u64 hv_do_hypercall(u64 control, void *inputaddr, void *outputaddr);
 extern u64 hv_do_fast_hypercall8(u16 control, u64 input8);
 extern bool hv_isolation_type_snp(void);
 extern bool hv_isolation_type_en_snp(void);
+bool hv_isolation_type_tdx(void);
 
 /* Helper functions that provide a consistent pattern for checking Hyper-V hypercall status. */
 static inline int hv_result(u64 status)