x86/tdx: Introduce wrappers to read and write TD metadata

The TDG_VM_WR TDCALL is used to ask the TDX module to change some
TD-specific VM configuration. There is currently only one user in the
kernel of this TDCALL leaf.  More will be added shortly.

Refactor to make way for more users of TDG_VM_WR who will need to modify
other TD configuration values.

Add a wrapper for the TDG_VM_RD TDCALL that requests TD-specific
metadata from the TDX module. There are currently no users for
TDG_VM_RD. Mark it as __maybe_unused until the first user appears.

This is preparation for enumeration and enabling optional TD features.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Link: https://lore.kernel.org/all/20241104103803.195705-2-kirill.shutemov%40linux.intel.com

1 files changed, 27 insertions, 5 deletions

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index 327c45c5013f..c74bb9e7d7a3 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -78,6 +78,32 @@ static inline void tdcall(u64 fn, struct tdx_module_args *args)
 		panic("TDCALL %lld failed (Buggy TDX module!)\n", fn);
 }
 
+/* Read TD-scoped metadata */
+static inline u64 __maybe_unused tdg_vm_rd(u64 field, u64 *value)
+{
+	struct tdx_module_args args = {
+		.rdx = field,
+	};
+	u64 ret;
+
+	ret = __tdcall_ret(TDG_VM_RD, &args);
+	*value = args.r8;
+
+	return ret;
+}
+
+/* Write TD-scoped metadata */
+static inline u64 tdg_vm_wr(u64 field, u64 value, u64 mask)
+{
+	struct tdx_module_args args = {
+		.rdx = field,
+		.r8 = value,
+		.r9 = mask,
+	};
+
+	return __tdcall(TDG_VM_WR, &args);
+}
+
 /**
  * tdx_mcall_get_report0() - Wrapper to get TDREPORT0 (a.k.a. TDREPORT
  *                           subtype 0) using TDG.MR.REPORT TDCALL.
@@ -929,10 +955,6 @@ static void tdx_kexec_finish(void)
 
 void __init tdx_early_init(void)
 {
-	struct tdx_module_args args = {
-		.rdx = TDCS_NOTIFY_ENABLES,
-		.r9 = -1ULL,
-	};
 	u64 cc_mask;
 	u32 eax, sig[3];
 
@@ -951,7 +973,7 @@ void __init tdx_early_init(void)
 	cc_set_mask(cc_mask);
 
 	/* Kernel does not use NOTIFY_ENABLES and does not need random #VEs */
-	tdcall(TDG_VM_WR, &args);
+	tdg_vm_wr(TDCS_NOTIFY_ENABLES, 0, -1ULL);
 
 	/*
 	 * All bits above GPA width are reserved and kernel treats shared bit