x86/tdx: Make TDX_HYPERCALL asm similar to TDX_MODULE_CALL

Now the 'struct tdx_hypercall_args' and 'struct tdx_module_args' are
almost the same, and the TDX_HYPERCALL and TDX_MODULE_CALL asm macro
share similar code pattern too.  The __tdx_hypercall() and __tdcall()
should be unified to use the same assembly code.

As a preparation to unify them, simplify the TDX_HYPERCALL to make it
more like the TDX_MODULE_CALL.

The TDX_HYPERCALL takes the pointer of 'struct tdx_hypercall_args' as
function call argument, and does below extra things comparing to the
TDX_MODULE_CALL:

1) It sets RAX to 0 (TDG.VP.VMCALL leaf) internally;
2) It sets RCX to the (fixed) bitmap of shared registers internally;
3) It calls __tdx_hypercall_failed() internally (and panics) when the
   TDCALL instruction itself fails;
4) After TDCALL, it moves R10 to RAX to return the return code of the
   VMCALL leaf, regardless the '\ret' asm macro argument;

Firstly, change the TDX_HYPERCALL to take the same function call
arguments as the TDX_MODULE_CALL does: TDCALL leaf ID, and the pointer
to 'struct tdx_module_args'.  Then 1) and 2) can be moved to the
caller:

 - TDG.VP.VMCALL leaf ID can be passed via the function call argument;
 - 'struct tdx_module_args' is 'struct tdx_hypercall_args' + RCX, thus
   the bitmap of shared registers can be passed via RCX in the
   structure.

Secondly, to move 3) and 4) out of assembly, make the TDX_HYPERCALL
always save output registers to the structure.  The caller then can:

 - Call __tdx_hypercall_failed() when TDX_HYPERCALL returns error;
 - Return R10 in the structure as the return code of the VMCALL leaf;

With above changes, change the asm function from __tdx_hypercall() to
__tdcall_hypercall(), and reimplement __tdx_hypercall() as the C wrapper
of it.  This avoids having to add another wrapper of __tdx_hypercall()
(_tdx_hypercall() is already taken).

The __tdcall_hypercall() will be replaced with a __tdcall() variant
using TDX_MODULE_CALL in a later commit as the final goal is to have one
assembly to handle both TDCALL and TDVMCALL.

Currently, the __tdx_hypercall() asm is in '.noinstr.text'.  To keep
this unchanged, annotate __tdx_hypercall(), which is a C function now,
as 'noinstr'.

Remove the __tdx_hypercall_ret() as __tdx_hypercall() already does so.

Implement __tdx_hypercall() in tdx-shared.c so it can be shared with the
compressed code.

Opportunistically fix a checkpatch error complaining using space around
parenthesis '(' and ')' while moving the bitmap of shared registers to
<asm/shared/tdx.h>.

[ dhansen: quash new calls of __tdx_hypercall_ret() that showed up ]

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Kai Huang <kai.huang@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/all/0cbf25e7aee3256288045023a31f65f0cef90af4.1692096753.git.kai.huang%40intel.com

1 files changed, 57 insertions, 29 deletions

diff --git a/arch/x86/include/asm/shared/tdx.h b/arch/x86/include/asm/shared/tdx.h
index 669749a22d8c..85493c4813cf 100644
--- a/arch/x86/include/asm/shared/tdx.h
+++ b/arch/x86/include/asm/shared/tdx.h
@@ -11,6 +11,7 @@
 #define TDX_IDENT		"IntelTDX    "
 
 /* TDX module Call Leaf IDs */
+#define TDG_VP_VMCALL			0
 #define TDG_VP_INFO			1
 #define TDG_VP_VEINFO_GET		3
 #define TDG_MR_REPORT			4
@@ -26,9 +27,64 @@
 
 #define TDVMCALL_STATUS_RETRY		1
 
+/*
+ * Bitmasks of exposed registers (with VMM).
+ */
+#define TDX_RDX		BIT(2)
+#define TDX_RBX		BIT(3)
+#define TDX_RSI		BIT(6)
+#define TDX_RDI		BIT(7)
+#define TDX_R8		BIT(8)
+#define TDX_R9		BIT(9)
+#define TDX_R10		BIT(10)
+#define TDX_R11		BIT(11)
+#define TDX_R12		BIT(12)
+#define TDX_R13		BIT(13)
+#define TDX_R14		BIT(14)
+#define TDX_R15		BIT(15)
+
+/*
+ * These registers are clobbered to hold arguments for each
+ * TDVMCALL. They are safe to expose to the VMM.
+ * Each bit in this mask represents a register ID. Bit field
+ * details can be found in TDX GHCI specification, section
+ * titled "TDCALL [TDG.VP.VMCALL] leaf".
+ */
+#define TDVMCALL_EXPOSE_REGS_MASK	\
+	(TDX_RDX | TDX_RBX | TDX_RSI | TDX_RDI | TDX_R8  | TDX_R9  | \
+	 TDX_R10 | TDX_R11 | TDX_R12 | TDX_R13 | TDX_R14 | TDX_R15)
+
 #ifndef __ASSEMBLY__
 
 /*
+ * Used in __tdcall*() to gather the input/output registers' values of the
+ * TDCALL instruction when requesting services from the TDX module. This is a
+ * software only structure and not part of the TDX module/VMM ABI
+ */
+struct tdx_module_args {
+	/* callee-clobbered */
+	u64 rcx;
+	u64 rdx;
+	u64 r8;
+	u64 r9;
+	/* extra callee-clobbered */
+	u64 r10;
+	u64 r11;
+	/* callee-saved + rdi/rsi */
+	u64 r12;
+	u64 r13;
+	u64 r14;
+	u64 r15;
+	u64 rbx;
+	u64 rdi;
+	u64 rsi;
+};
+
+/* Used to communicate with the TDX module */
+u64 __tdcall(u64 fn, struct tdx_module_args *args);
+u64 __tdcall_ret(u64 fn, struct tdx_module_args *args);
+
+/*
  * Used in __tdx_hypercall() to pass down and get back registers' values of
  * the TDCALL instruction when requesting services from the VMM.
  *
@@ -50,8 +106,8 @@ struct tdx_hypercall_args {
 };
 
 /* Used to request services from the VMM */
+u64 __tdcall_hypercall(u64 fn, struct tdx_module_args *args);
 u64 __tdx_hypercall(struct tdx_hypercall_args *args);
-u64 __tdx_hypercall_ret(struct tdx_hypercall_args *args);
 
 /*
  * Wrapper for standard use of __tdx_hypercall with no output aside from
@@ -75,34 +131,6 @@ static inline u64 _tdx_hypercall(u64 fn, u64 r12, u64 r13, u64 r14, u64 r15)
 /* Called from __tdx_hypercall() for unrecoverable failure */
 void __tdx_hypercall_failed(void);
 
-/*
- * Used in __tdcall*() to gather the input/output registers' values of the
- * TDCALL instruction when requesting services from the TDX module. This is a
- * software only structure and not part of the TDX module/VMM ABI
- */
-struct tdx_module_args {
-	/* callee-clobbered */
-	u64 rcx;
-	u64 rdx;
-	u64 r8;
-	u64 r9;
-	/* extra callee-clobbered */
-	u64 r10;
-	u64 r11;
-	/* callee-saved + rdi/rsi */
-	u64 r12;
-	u64 r13;
-	u64 r14;
-	u64 r15;
-	u64 rbx;
-	u64 rdi;
-	u64 rsi;
-};
-
-/* Used to communicate with the TDX module */
-u64 __tdcall(u64 fn, struct tdx_module_args *args);
-u64 __tdcall_ret(u64 fn, struct tdx_module_args *args);
-
 bool tdx_accept_memory(phys_addr_t start, phys_addr_t end);
 
 /*