x86/hyperv: Support hypercalls for fully enlightened TDX guests

A fully enlightened TDX guest on Hyper-V (i.e. without the paravisor) only
uses the GHCI call rather than hv_hypercall_pg. Do not initialize
hypercall_pg for such a guest.

In hv_common_cpu_init(), the hyperv_pcpu_input_arg page needs to be
decrypted in such a guest.
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
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/20230824080712.30327-3-decui@microsoft.com

arch/x86/hyperv/hv_init.c

@@ -476,6 +476,10 @@ void __init hyperv_init(void)
 	/* 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);
 
+	/* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
+	if (hv_isolation_type_tdx())
+		goto skip_hypercall_pg_init;
+
 	hv_hypercall_pg = __vmalloc_node_range(PAGE_SIZE, 1, VMALLOC_START,
 			VMALLOC_END, GFP_KERNEL, PAGE_KERNEL_ROX,
 			VM_FLUSH_RESET_PERMS, NUMA_NO_NODE,
@@ -515,6 +519,7 @@ void __init hyperv_init(void)
 		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 	}
 
+skip_hypercall_pg_init:
 	/*
 	 * hyperv_init() is called before LAPIC is initialized: see
 	 * apic_intr_mode_init() -> x86_platform.apic_post_init() and
@@ -642,6 +647,9 @@ bool hv_is_hyperv_initialized(void)
 	if (x86_hyper_type != X86_HYPER_MS_HYPERV)
 		return false;
 
+	/* A TDX guest uses the GHCI call rather than hv_hypercall_pg. */
+	if (hv_isolation_type_tdx())
+		return true;
 	/*
 	 * Verify that earlier initialization succeeded by checking
 	 * that the hypercall page is setup

arch/x86/hyperv/ivm.c

@@ -571,3 +571,20 @@ bool hv_isolation_type_tdx(void)
 {
 	return static_branch_unlikely(&isolation_type_tdx);
 }
+
+#ifdef CONFIG_INTEL_TDX_GUEST
+
+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
+{
+	struct tdx_hypercall_args args = { };
+
+	args.r10 = control;
+	args.rdx = param1;
+	args.r8  = param2;
+
+	(void)__tdx_hypercall_ret(&args);
+
+	return args.r11;
+}
+
+#endif

arch/x86/include/asm/mshyperv.h

@@ -51,6 +51,7 @@ extern union hv_ghcb * __percpu *hv_ghcb_pg;
 
 extern bool hv_isolation_type_en_snp(void);
 bool hv_isolation_type_tdx(void);
+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
 
 /*
  * DEFAULT INIT GPAT and SEGMENT LIMIT value in struct VMSA
@@ -63,6 +64,10 @@ int hv_call_deposit_pages(int node, u64 partition_id, u32 num_pages);
 int hv_call_add_logical_proc(int node, u32 lp_index, u32 acpi_id);
 int hv_call_create_vp(int node, u64 partition_id, u32 vp_index, u32 flags);
 
+/*
+ * If the hypercall involves no input or output parameters, the hypervisor
+ * ignores the corresponding GPA pointer.
+ */
 static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
 {
 	u64 input_address = input ? virt_to_phys(input) : 0;
@@ -70,6 +75,9 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
 	u64 hv_status;
 
 #ifdef CONFIG_X86_64
+	if (hv_isolation_type_tdx())
+		return hv_tdx_hypercall(control, input_address, output_address);
+
 	if (hv_isolation_type_en_snp()) {
 		__asm__ __volatile__("mov %4, %%r8\n"
 				     "vmmcall"
@@ -123,6 +131,9 @@ static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
 	u64 hv_status;
 
 #ifdef CONFIG_X86_64
+	if (hv_isolation_type_tdx())
+		return hv_tdx_hypercall(control, input1, 0);
+
 	if (hv_isolation_type_en_snp()) {
 		__asm__ __volatile__(
 				"vmmcall"
@@ -174,6 +185,9 @@ static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
 	u64 hv_status;
 
 #ifdef CONFIG_X86_64
+	if (hv_isolation_type_tdx())
+		return hv_tdx_hypercall(control, input1, input2);
+
 	if (hv_isolation_type_en_snp()) {
 		__asm__ __volatile__("mov %4, %%r8\n"
 				     "vmmcall"

drivers/hv/hv_common.c

@@ -381,10 +381,10 @@ int hv_common_cpu_init(unsigned int cpu)
 			*outputarg = (char *)(*inputarg) + HV_HYP_PAGE_SIZE;
 		}
 
-		if (hv_isolation_type_en_snp()) {
+		if (hv_isolation_type_en_snp() || hv_isolation_type_tdx()) {
 			ret = set_memory_decrypted((unsigned long)*inputarg, pgcount);
 			if (ret) {
-				kfree(*inputarg);
+				/* It may be unsafe to free *inputarg */
 				*inputarg = NULL;
 				return ret;
 			}
@@ -567,3 +567,9 @@ u64 __weak hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_s
 	return HV_STATUS_INVALID_PARAMETER;
 }
 EXPORT_SYMBOL_GPL(hv_ghcb_hypercall);
+
+u64 __weak hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
+{
+	return HV_STATUS_INVALID_PARAMETER;
+}
+EXPORT_SYMBOL_GPL(hv_tdx_hypercall);

include/asm-generic/mshyperv.h

@@ -283,6 +283,7 @@ enum hv_isolation_type hv_get_isolation_type(void);
 bool hv_is_isolation_supported(void);
 bool hv_isolation_type_snp(void);
 u64 hv_ghcb_hypercall(u64 control, void *input, void *output, u32 input_size);
+u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
 void hyperv_cleanup(void);
 bool hv_query_ext_cap(u64 cap_query);
 void hv_setup_dma_ops(struct device *dev, bool coherent);