x86/hyperv: Use TDX GHCI to access some MSRs in a TDX VM with the paravisor

When the paravisor is present, a SNP VM must use GHCB to access some
special MSRs, including HV_X64_MSR_GUEST_OS_ID and some SynIC MSRs.

Similarly, when the paravisor is present, a TDX VM must use TDX GHCI
to access the same MSRs.

Implement hv_tdx_msr_write() and hv_tdx_msr_read(), and use the helper
functions hv_ivm_msr_read() and hv_ivm_msr_write() to access the MSRs
in a unified way for SNP/TDX VMs with the paravisor.

Do not export hv_tdx_msr_write() and hv_tdx_msr_read(), because we never
really used hv_ghcb_msr_write() and hv_ghcb_msr_read() in any module.

Update arch/x86/include/asm/mshyperv.h so that the kernel can still build
if CONFIG_AMD_MEM_ENCRYPT or CONFIG_INTEL_TDX_GUEST is not set, or
neither is set.
Signed-off-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230824080712.30327-9-decui@microsoft.com

arch/x86/hyperv/hv_init.c

@@ -500,8 +500,8 @@ void __init hyperv_init(void)
 	guest_id = hv_generate_guest_id(LINUX_VERSION_CODE);
 	wrmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
 
-	/* Hyper-V requires to write guest os id via ghcb in SNP IVM. */
-	hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
+	/* With the paravisor, the VM must also write the ID via GHCB/GHCI */
+	hv_ivm_msr_write(HV_X64_MSR_GUEST_OS_ID, guest_id);
 
 	/* A TDX VM with no paravisor only uses TDX GHCI rather than hv_hypercall_pg */
 	if (hv_isolation_type_tdx() && !ms_hyperv.paravisor_present)
@@ -590,7 +590,7 @@ void __init hyperv_init(void)
 
 clean_guest_os_id:
 	wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
-	hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
+	hv_ivm_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
 	cpuhp_remove_state(cpuhp);
 free_ghcb_page:
 	free_percpu(hv_ghcb_pg);
@@ -611,7 +611,7 @@ void hyperv_cleanup(void)
 
 	/* Reset our OS id */
 	wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
-	hv_ghcb_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
+	hv_ivm_msr_write(HV_X64_MSR_GUEST_OS_ID, 0);
 
 	/*
 	 * Reset hypercall page reference before reset the page,

arch/x86/hyperv/ivm.c

@@ -24,6 +24,7 @@
 #include <asm/realmode.h>
 #include <asm/e820/api.h>
 #include <asm/desc.h>
+#include <uapi/asm/vmx.h>
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 
@@ -186,7 +187,7 @@ bool hv_ghcb_negotiate_protocol(void)
 	return true;
 }
 
-void hv_ghcb_msr_write(u64 msr, u64 value)
+static void hv_ghcb_msr_write(u64 msr, u64 value)
 {
 	union hv_ghcb *hv_ghcb;
 	void **ghcb_base;
@@ -214,9 +215,8 @@ void hv_ghcb_msr_write(u64 msr, u64 value)
 
 	local_irq_restore(flags);
 }
-EXPORT_SYMBOL_GPL(hv_ghcb_msr_write);
 
-void hv_ghcb_msr_read(u64 msr, u64 *value)
+static void hv_ghcb_msr_read(u64 msr, u64 *value)
 {
 	union hv_ghcb *hv_ghcb;
 	void **ghcb_base;
@@ -246,10 +246,71 @@ void hv_ghcb_msr_read(u64 msr, u64 *value)
 			| ((u64)lower_32_bits(hv_ghcb->ghcb.save.rdx) << 32);
 	local_irq_restore(flags);
 }
-EXPORT_SYMBOL_GPL(hv_ghcb_msr_read);
 
+#else
+static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
+static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
 #endif /* CONFIG_AMD_MEM_ENCRYPT */
 
+#ifdef CONFIG_INTEL_TDX_GUEST
+static void hv_tdx_msr_write(u64 msr, u64 val)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = EXIT_REASON_MSR_WRITE,
+		.r12 = msr,
+		.r13 = val,
+	};
+
+	u64 ret = __tdx_hypercall(&args);
+
+	WARN_ONCE(ret, "Failed to emulate MSR write: %lld\n", ret);
+}
+
+static void hv_tdx_msr_read(u64 msr, u64 *val)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = EXIT_REASON_MSR_READ,
+		.r12 = msr,
+	};
+
+	u64 ret = __tdx_hypercall_ret(&args);
+
+	if (WARN_ONCE(ret, "Failed to emulate MSR read: %lld\n", ret))
+		*val = 0;
+	else
+		*val = args.r11;
+}
+#else
+static inline void hv_tdx_msr_write(u64 msr, u64 value) {}
+static inline void hv_tdx_msr_read(u64 msr, u64 *value) {}
+#endif /* CONFIG_INTEL_TDX_GUEST */
+
+#if defined(CONFIG_AMD_MEM_ENCRYPT) || defined(CONFIG_INTEL_TDX_GUEST)
+void hv_ivm_msr_write(u64 msr, u64 value)
+{
+	if (!ms_hyperv.paravisor_present)
+		return;
+
+	if (hv_isolation_type_tdx())
+		hv_tdx_msr_write(msr, value);
+	else if (hv_isolation_type_snp())
+		hv_ghcb_msr_write(msr, value);
+}
+
+void hv_ivm_msr_read(u64 msr, u64 *value)
+{
+	if (!ms_hyperv.paravisor_present)
+		return;
+
+	if (hv_isolation_type_tdx())
+		hv_tdx_msr_read(msr, value);
+	else if (hv_isolation_type_snp())
+		hv_ghcb_msr_read(msr, value);
+}
+#endif
+
 #if defined(CONFIG_AMD_MEM_ENCRYPT) || defined(CONFIG_INTEL_TDX_GUEST)
 /*
  * hv_mark_gpa_visibility - Set pages visible to host via hvcall.

arch/x86/include/asm/mshyperv.h

@@ -275,14 +275,10 @@ int hv_map_ioapic_interrupt(int ioapic_id, bool level, int vcpu, int vector,
 int hv_unmap_ioapic_interrupt(int ioapic_id, struct hv_interrupt_entry *entry);
 
 #ifdef CONFIG_AMD_MEM_ENCRYPT
-void hv_ghcb_msr_write(u64 msr, u64 value);
-void hv_ghcb_msr_read(u64 msr, u64 *value);
 bool hv_ghcb_negotiate_protocol(void);
 void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
 int hv_snp_boot_ap(int cpu, unsigned long start_ip);
 #else
-static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
-static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
 static inline bool hv_ghcb_negotiate_protocol(void) { return false; }
 static inline void hv_ghcb_terminate(unsigned int set, unsigned int reason) {}
 static inline int hv_snp_boot_ap(int cpu, unsigned long start_ip) { return 0; }
@@ -292,8 +288,12 @@ extern bool hv_isolation_type_snp(void);
 
 #if defined(CONFIG_AMD_MEM_ENCRYPT) || defined(CONFIG_INTEL_TDX_GUEST)
 void hv_vtom_init(void);
+void hv_ivm_msr_write(u64 msr, u64 value);
+void hv_ivm_msr_read(u64 msr, u64 *value);
 #else
 static inline void hv_vtom_init(void) {}
+static inline void hv_ivm_msr_write(u64 msr, u64 value) {}
+static inline void hv_ivm_msr_read(u64 msr, u64 *value) {}
 #endif
 
 static inline bool hv_is_synic_reg(unsigned int reg)

arch/x86/kernel/cpu/mshyperv.c

@@ -70,8 +70,8 @@ u64 hv_get_non_nested_register(unsigned int reg)
 {
 	u64 value;
 
-	if (hv_is_synic_reg(reg) && hv_isolation_type_snp())
-		hv_ghcb_msr_read(reg, &value);
+	if (hv_is_synic_reg(reg) && ms_hyperv.paravisor_present)
+		hv_ivm_msr_read(reg, &value);
 	else
 		rdmsrl(reg, value);
 	return value;
@@ -80,8 +80,8 @@ EXPORT_SYMBOL_GPL(hv_get_non_nested_register);
 
 void hv_set_non_nested_register(unsigned int reg, u64 value)
 {
-	if (hv_is_synic_reg(reg) && hv_isolation_type_snp()) {
-		hv_ghcb_msr_write(reg, value);
+	if (hv_is_synic_reg(reg) && ms_hyperv.paravisor_present) {
+		hv_ivm_msr_write(reg, value);
 
 		/* Write proxy bit via wrmsl instruction */
 		if (hv_is_sint_reg(reg))