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From:   "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>
Subject: [PATCHv8 19/30] x86/tdx: Wire up KVM hypercalls
Date:   Wed,  6 Apr 2022 02:29:28 +0300
Message-Id: <20220405232939.73860-20-kirill.shutemov@linux.intel.com>
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From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

KVM hypercalls use the VMCALL or VMMCALL instructions. Although the ABI
is similar, those instructions no longer function for TDX guests.

Make vendor-specific TDVMCALLs instead of VMCALL. This enables TDX
guests to run with KVM acting as the hypervisor.

Among other things, KVM hypercall is used to send IPIs.

Since the KVM driver can be built as a kernel module, export
tdx_kvm_hypercall() to make the symbols visible to kvm.ko.

Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
---
 arch/x86/coco/tdx/tdx.c         | 17 +++++++++++++++++
 arch/x86/include/asm/kvm_para.h | 22 ++++++++++++++++++++++
 arch/x86/include/asm/tdx.h      | 11 +++++++++++
 3 files changed, 50 insertions(+)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index cc14b7c0c157..f50f530aff5f 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -64,6 +64,23 @@ static u64 hcall_func(u64 exit_reason)
 	return exit_reason;
 }
 
+#ifdef CONFIG_KVM_GUEST
+long tdx_kvm_hypercall(unsigned int nr, unsigned long p1, unsigned long p2,
+		       unsigned long p3, unsigned long p4)
+{
+	struct tdx_hypercall_args args = {
+		.r10 = nr,
+		.r11 = p1,
+		.r12 = p2,
+		.r13 = p3,
+		.r14 = p4,
+	};
+
+	return __tdx_hypercall(&args, 0);
+}
+EXPORT_SYMBOL_GPL(tdx_kvm_hypercall);
+#endif
+
 /*
  * Used for TDX guests to make calls directly to the TD module.  This
  * should only be used for calls that have no legitimate reason to fail
diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 56935ebb1dfe..57bc74e112f2 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -7,6 +7,8 @@
 #include <linux/interrupt.h>
 #include <uapi/asm/kvm_para.h>
 
+#include <asm/tdx.h>
+
 #ifdef CONFIG_KVM_GUEST
 bool kvm_check_and_clear_guest_paused(void);
 #else
@@ -32,6 +34,10 @@ static inline bool kvm_check_and_clear_guest_paused(void)
 static inline long kvm_hypercall0(unsigned int nr)
 {
 	long ret;
+
+	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return tdx_kvm_hypercall(nr, 0, 0, 0, 0);
+
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
 		     : "a"(nr)
@@ -42,6 +48,10 @@ static inline long kvm_hypercall0(unsigned int nr)
 static inline long kvm_hypercall1(unsigned int nr, unsigned long p1)
 {
 	long ret;
+
+	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return tdx_kvm_hypercall(nr, p1, 0, 0, 0);
+
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
 		     : "a"(nr), "b"(p1)
@@ -53,6 +63,10 @@ static inline long kvm_hypercall2(unsigned int nr, unsigned long p1,
 				  unsigned long p2)
 {
 	long ret;
+
+	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return tdx_kvm_hypercall(nr, p1, p2, 0, 0);
+
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
 		     : "a"(nr), "b"(p1), "c"(p2)
@@ -64,6 +78,10 @@ static inline long kvm_hypercall3(unsigned int nr, unsigned long p1,
 				  unsigned long p2, unsigned long p3)
 {
 	long ret;
+
+	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return tdx_kvm_hypercall(nr, p1, p2, p3, 0);
+
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
 		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3)
@@ -76,6 +94,10 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
 				  unsigned long p4)
 {
 	long ret;
+
+	if (cpu_feature_enabled(X86_FEATURE_TDX_GUEST))
+		return tdx_kvm_hypercall(nr, p1, p2, p3, p4);
+
 	asm volatile(KVM_HYPERCALL
 		     : "=a"(ret)
 		     : "a"(nr), "b"(p1), "c"(p2), "d"(p3), "S"(p4)
diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 9ffd0d2e6e0f..020c81a7c729 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -76,5 +76,16 @@ static inline bool tdx_early_handle_ve(struct pt_regs *regs) { return false; }
 
 #endif /* CONFIG_INTEL_TDX_GUEST */
 
+#if defined(CONFIG_KVM_GUEST) && defined(CONFIG_INTEL_TDX_GUEST)
+long tdx_kvm_hypercall(unsigned int nr, unsigned long p1, unsigned long p2,
+		       unsigned long p3, unsigned long p4);
+#else
+static inline long tdx_kvm_hypercall(unsigned int nr, unsigned long p1,
+				     unsigned long p2, unsigned long p3,
+				     unsigned long p4)
+{
+	return -ENODEV;
+}
+#endif /* CONFIG_INTEL_TDX_GUEST && CONFIG_KVM_GUEST */
 #endif /* !__ASSEMBLY__ */
 #endif /* _ASM_X86_TDX_H */
-- 
2.35.1