[PATCH v4 3/8] x86/virt/tdx: Prepare to support reading other global metadata fields

[Kai Huang <kai.huang@intel.com>]

The TDX module provides a set of "Global Metadata Fields".  They report
things like TDX module version, supported features, and fields related
to create/run TDX guests and so on.  TDX supports 8/16/32/64 bits
metadata field element sizes.  For a given metadata field, the element
size is encoded in the metadata field ID.

For now the kernel only reads "TD Memory Region" (TDMR) related metadata
fields and they are all 16-bit.  Thus the kernel only has one primitive
__read_sys_metadata_field16() to read 16-bit metadata field and the
macro, read_sys_metadata_field16(), which does additional build-time
check of the field ID makes sure the field is indeed 16-bit.

Future changes will need to read more metadata fields with different
element sizes.  Choose to provide one primitive for each element size to
support that.  Similar to the build_mmio_read() macro, reimplement the
body of __read_sys_metadata_field16() as a macro build_sysmd_read(_size)
in size-agnostic way, so it can be used to generate one primitive for
each element size:

  build_sysmd_read(8)
  build_sysmd_read(16)
  ..

Also extend read_sys_metadata_field16() take the '_size' as argument
(and rename it to read_sys_metadata_field() to make it size-agnostic) to
allow the READ_SYS_INFO() macro to choose which primitive to use.

Signed-off-by: Kai Huang <kai.huang@intel.com>
---

v3 -> v4:
 - Change to use one primitive for each element size, similar to
   build_mmio_read() macro - Dan.
 - Rewrite changelog based on the new code.
 - "global metadata fields" -> "Global Metadata Fields" - Ardian.

v2 -> v3:
 - Rename read_sys_metadata_field() to tdh_sys_rd() so the former can be
   used as the high level wrapper.  Get rid of "stbuf_" prefix since
   people don't like it.
 
 - Rewrite after removing 'struct field_mapping' and reimplementing
   TD_SYSINFO_MAP().
 
---
 arch/x86/virt/vmx/tdx/tdx.c | 40 ++++++++++++++++++++-----------------
 1 file changed, 22 insertions(+), 18 deletions(-)

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 2f7e4abc1bb9..b5c8dde9caf0 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -250,7 +250,7 @@ static int build_tdx_memlist(struct list_head *tmb_list)
 	return ret;
 }
 
-static int read_sys_metadata_field(u64 field_id, u64 *data)
+static int tdh_sys_rd(u64 field_id, u64 *data)
 {
 	struct tdx_module_args args = {};
 	int ret;
@@ -270,25 +270,29 @@ static int read_sys_metadata_field(u64 field_id, u64 *data)
 	return 0;
 }
 
-static int __read_sys_metadata_field16(u64 field_id, u16 *val)
-{
-	u64 tmp;
-	int ret;
-
-	ret = read_sys_metadata_field(field_id, &tmp);
-	if (ret)
-		return ret;
-
-	*val = tmp;
-
-	return 0;
+#define build_sysmd_read(_size)							\
+static int __read_sys_metadata_field##_size(u64 field_id, u##_size *val)	\
+{										\
+	u64 tmp;								\
+	int ret;								\
+										\
+	ret = tdh_sys_rd(field_id, &tmp);					\
+	if (ret)								\
+		return ret;							\
+										\
+	*val = tmp;								\
+										\
+	return 0;								\
 }
 
-#define read_sys_metadata_field16(_field_id, _val)		\
+build_sysmd_read(16)
+
+#define read_sys_metadata_field(_field_id, _val, _size)		\
 ({								\
 	BUILD_BUG_ON(MD_FIELD_ID_ELE_SIZE_CODE(_field_id) !=	\
-			MD_FIELD_ID_ELE_SIZE_16BIT);		\
-	__read_sys_metadata_field16(_field_id, _val);		\
+			MD_FIELD_ID_ELE_SIZE_##_size##BIT);	\
+	BUILD_BUG_ON(_size != sizeof(*_val) * 8);		\
+	__read_sys_metadata_field##_size(_field_id, _val);	\
 })
 
 static int get_tdx_sys_info_tdmr(struct tdx_sys_info_tdmr *sysinfo_tdmr)
@@ -296,8 +300,8 @@ static int get_tdx_sys_info_tdmr(struct tdx_sys_info_tdmr *sysinfo_tdmr)
 	int ret = 0;
 
 #define READ_SYS_INFO(_field_id, _member)				\
-	ret = ret ?: read_sys_metadata_field16(MD_FIELD_ID_##_field_id,	\
-					&sysinfo_tdmr->_member)
+	ret = ret ?: read_sys_metadata_field(MD_FIELD_ID_##_field_id,	\
+					&sysinfo_tdmr->_member, 16)
 
 	READ_SYS_INFO(MAX_TDMRS,	     max_tdmrs);
 	READ_SYS_INFO(MAX_RESERVED_PER_TDMR, max_reserved_per_tdmr);
-- 
2.46.0