[PATCH v1 3/8] x86/virt/tdx: Add a table-driven TDX global metadata reader

[Chao Gao <chao.gao@intel.com>]

From: Dave Hansen <dave@sr71.net>

The auto-generated tdx_global_metadata.c populates each member of
'struct tdx_sys_info' with a chain like

	if (!ret && !(ret = read_sys_metadata_field(0x..., &val)))
		sysinfo_xxx->member = val;

repeated once per field, with a bare hex literal for the field ID and an
implicit narrowing assignment.  Reading it requires the JSON file, and
reviewing any change to it requires the out-of-tree script.

Replace it with a small table-driven reader. Each table entry pairs
a named MD_FIELD_ID_* with the C member that holds its value:

	#define MAP_FEATURES(_field_id, _member)	\
		TD_SYSINFO_MAP(_field_id, tdx_sys_info_features, _member)

	static const struct tdx_sys_field features_fields[] __initconst = {
		MAP_FEATURES(TDX_FEATURES0,	tdx_features0),
	};

TD_SYSINFO_MAP() derives the destination offset and width from the
struct via offsetof()/sizeof_field().

Add read_sys_metadata_table() to walk such a table, reading each field
and populating the C struct.

Three things fall out of this table-driven reader, all of which matter now
that the code is hand-maintained rather than auto-generated:

  - The field-to-member pairing becomes data rather than code embedded
    in control flow.
  - The read logic exists once instead of once per field.
  - The width is recorded explicitly instead of being implied by a
    narrowing assignment.

Convert the 'features' class only, as an example. The remaining classes
follow in later patches.

Assisted-by: Claude:claude-opus-5
Not-yet-signed-off-by: Dave Hansen <dave@sr71.net>
Signed-off-by: Chao Gao <chao.gao@intel.com>
---
 arch/x86/virt/vmx/tdx/tdx.c                 | 60 +++++++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx_global_metadata.c | 11 ----
 2 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 42df8ea464c4..fb21433e7851 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -347,6 +347,66 @@ static int read_sys_metadata_field(u64 field_id, u64 *data)
 	return 0;
 }
 
+/*
+ * Mapping between a TDX global metadata field and the C member that
+ * holds its value. Use TD_SYSINFO_MAP() to populate entries.
+ */
+struct tdx_sys_field {
+	u64 field_id;
+	u16 offset;
+	u8  size;
+};
+
+#define TD_SYSINFO_MAP(_field_id, _struct, _member)				\
+	{									\
+		.field_id = MD_FIELD_ID_##_field_id,				\
+		.offset   = offsetof(struct _struct, _member),			\
+		.size     = sizeof_field(struct _struct, _member),		\
+	}
+
+/*
+ * Walk a table of TDX global metadata fields, read each via TDH.SYS.RD,
+ * and store the result into the matching C member of *@base.
+ */
+static int read_sys_metadata_table(const struct tdx_sys_field *fields,
+				   int nr_fields, void *base)
+{
+	int i, ret;
+	u64 val;
+
+	for (i = 0; i < nr_fields; i++) {
+		const struct tdx_sys_field *f = &fields[i];
+
+		ret = read_sys_metadata_field(f->field_id, &val);
+		if (ret)
+			return ret;
+
+		switch (f->size) {
+		case 1: *(u8  *)(base + f->offset) = val; break;
+		case 2: *(u16 *)(base + f->offset) = val; break;
+		case 4: *(u32 *)(base + f->offset) = val; break;
+		case 8: *(u64 *)(base + f->offset) = val; break;
+		default:
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
+#define MAP_FEATURES(_field_id, _member)	\
+	TD_SYSINFO_MAP(_field_id, tdx_sys_info_features, _member)
+
+static const struct tdx_sys_field features_fields[] __initconst = {
+	MAP_FEATURES(TDX_FEATURES0,	tdx_features0),
+};
+
+static __init int get_tdx_sys_info_features(struct tdx_sys_info_features *sysinfo_features)
+{
+	return read_sys_metadata_table(features_fields,
+				       ARRAY_SIZE(features_fields),
+				       sysinfo_features);
+}
+
 #include "tdx_global_metadata.c"
 
 static __init int check_features(struct tdx_sys_info *sysinfo)
diff --git a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
index e49c300f23d4..e69c655a91a0 100644
--- a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
+++ b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
@@ -22,17 +22,6 @@ static int get_tdx_sys_info_version(struct tdx_sys_info_version *sysinfo_version
 	return ret;
 }
 
-static __init int get_tdx_sys_info_features(struct tdx_sys_info_features *sysinfo_features)
-{
-	int ret = 0;
-	u64 val;
-
-	if (!ret && !(ret = read_sys_metadata_field(0x0A00000300000008, &val)))
-		sysinfo_features->tdx_features0 = val;
-
-	return ret;
-}
-
 static __init int get_tdx_sys_info_tdmr(struct tdx_sys_info_tdmr *sysinfo_tdmr)
 {
 	int ret = 0;
-- 
2.52.0