[PATCH 8/9] x86/hyperv: Use TDX GHCI to access some MSRs in a TDX VM with the paravisor

[Dexuan Cui <decui@microsoft.com>]

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_read_msr() and hv_tdx_write_msr(), 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.

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 arch/x86/hyperv/hv_init.c       |  8 ++--
 arch/x86/hyperv/ivm.c           | 72 +++++++++++++++++++++++++++++++--
 arch/x86/include/asm/mshyperv.h |  8 ++--
 arch/x86/kernel/cpu/mshyperv.c  |  8 ++--
 4 files changed, 80 insertions(+), 16 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 9c12a199ea62c..abd0a8bd3f15e 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -505,8 +505,8 @@ 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() && !hyperv_paravisor_present)
@@ -595,7 +595,7 @@ 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);
@@ -616,7 +616,7 @@ 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,
diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
index 0d54bc8b06b4a..b8fb1557c1986 100644
--- a/arch/x86/hyperv/ivm.c
+++ b/arch/x86/hyperv/ivm.c
@@ -184,7 +184,49 @@ bool hv_ghcb_negotiate_protocol(void)
 	return true;
 }
 
-void hv_ghcb_msr_write(u64 msr, u64 value)
+#define EXIT_REASON_MSR_READ		31
+#define EXIT_REASON_MSR_WRITE		32
+
+static void hv_tdx_read_msr(u64 msr, u64 *val)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = EXIT_REASON_MSR_READ,
+		.r12 = msr,
+	};
+
+#ifdef CONFIG_INTEL_TDX_GUEST
+	u64 ret = __tdx_hypercall_ret(&args);
+#else
+	u64 ret = HV_STATUS_INVALID_PARAMETER;
+#endif
+
+	if (WARN_ONCE(ret, "Failed to emulate MSR read: %lld\n", ret))
+		*val = 0;
+	else
+		*val = args.r11;
+}
+
+static void hv_tdx_write_msr(u64 msr, u64 val)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = TDX_HYPERCALL_STANDARD,
+		.r11 = EXIT_REASON_MSR_WRITE,
+		.r12 = msr,
+		.r13 = val,
+	};
+
+#ifdef CONFIG_INTEL_TDX_GUEST
+	u64 ret = __tdx_hypercall(&args);
+#else
+	u64 ret = HV_STATUS_INVALID_PARAMETER;
+	(void)args;
+#endif
+
+	WARN_ONCE(ret, "Failed to emulate MSR write: %lld\n", ret);
+}
+
+static void hv_ghcb_msr_write(u64 msr, u64 value)
 {
 	union hv_ghcb *hv_ghcb;
 	void **ghcb_base;
@@ -212,9 +254,20 @@ 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)
+void hv_ivm_msr_write(u64 msr, u64 value)
+{
+	if (!hyperv_paravisor_present)
+		return;
+
+	if (hv_isolation_type_tdx())
+		hv_tdx_write_msr(msr, value);
+	else if (hv_isolation_type_snp())
+		hv_ghcb_msr_write(msr, value);
+}
+EXPORT_SYMBOL_GPL(hv_ivm_msr_write);
+
+static void hv_ghcb_msr_read(u64 msr, u64 *value)
 {
 	union hv_ghcb *hv_ghcb;
 	void **ghcb_base;
@@ -244,7 +297,18 @@ 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);
+
+void hv_ivm_msr_read(u64 msr, u64 *value)
+{
+	if (!hyperv_paravisor_present)
+		return;
+
+	if (hv_isolation_type_tdx())
+		hv_tdx_read_msr(msr, value);
+	else if (hv_isolation_type_snp())
+		hv_ghcb_msr_read(msr, value);
+}
+EXPORT_SYMBOL_GPL(hv_ivm_msr_read);
 
 /*
  * hv_mark_gpa_visibility - Set pages visible to host via hvcall.
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index 9fa31dce69727..3f22324ef2e25 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -255,15 +255,15 @@ 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);
+void hv_ivm_msr_write(u64 msr, u64 value);
+void hv_ivm_msr_read(u64 msr, u64 *value);
 bool hv_ghcb_negotiate_protocol(void);
 void __noreturn hv_ghcb_terminate(unsigned int set, unsigned int reason);
 void hv_vtom_init(void);
 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 void hv_ivm_msr_write(u64 msr, u64 value) {}
+static inline void hv_ivm_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 void hv_vtom_init(void) {}
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index ddcc62185e4ae..fb585d3b080b1 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -72,8 +72,8 @@ 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) && hyperv_paravisor_present)
+		hv_ivm_msr_read(reg, &value);
 	else
 		rdmsrl(reg, value);
 	return value;
@@ -82,8 +82,8 @@ 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) && hyperv_paravisor_present) {
+		hv_ivm_msr_write(reg, value);
 
 		/* Write proxy bit via wrmsl instruction */
 		if (hv_is_sint_reg(reg))
-- 
2.25.1