[PATCH 3/6] x86/virt/tdx: Detect if the extensions initialization is required

[Xu Yilun]

Some add-on features require TDX module extensions. The TDX module
provides a metadata field "ext_required" to indicate this requirement.

Add the first step of TDX module extensions initialization by detecting
if the extensions are required:

  1. Check if the extensions are supported via TDX_FEATURES0_EXT. If
     not, ext_required is not readable.
  2. Check if any TDX feature needs the extensions via ext_required.

Skip the extensions initialization when it is not required.

Currently all metadata fields are read at the very beginning of TDX
module initialization. However, ext_required is only valid after the
add-on feature configuration, so it cannot use the existing metadata
reading method.

Add a dedicated metadata reading interface for the extensions, call it
after add-on feature configuration.

Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
Reviewed-by: Tony Lindgren <tony.lindgren@xxxxxxxxxxxxxxx>
---
v1:
 - Include struct tdx_sys_info_ext in struct tdx_sys_info.
---
 arch/x86/include/asm/tdx.h                  |  1 +
 arch/x86/include/asm/tdx_global_metadata.h  |  5 ++++
 arch/x86/virt/vmx/tdx/tdx.c                 | 28 +++++++++++++++++++++
 arch/x86/virt/vmx/tdx/tdx_global_metadata.c | 14 +++++++++++
 4 files changed, 48 insertions(+)

diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
index 89e97d5761d8..6657f2db0330 100644
--- a/arch/x86/include/asm/tdx.h
+++ b/arch/x86/include/asm/tdx.h
@@ -36,6 +36,7 @@
 /* Bit definitions of TDX_FEATURES0 metadata field */
 #define TDX_FEATURES0_TD_PRESERVING	BIT_ULL(1)
 #define TDX_FEATURES0_NO_RBP_MOD	BIT_ULL(18)
+#define TDX_FEATURES0_EXT		BIT_ULL(39)
 
 #ifndef __ASSEMBLER__
 
diff --git a/arch/x86/include/asm/tdx_global_metadata.h b/arch/x86/include/asm/tdx_global_metadata.h
index 41150d546589..fe3fe91de71f 100644
--- a/arch/x86/include/asm/tdx_global_metadata.h
+++ b/arch/x86/include/asm/tdx_global_metadata.h
@@ -44,12 +44,17 @@ struct tdx_sys_info_handoff {
 	u16 module_hv;
 };
 
+struct tdx_sys_info_ext {
+	bool ext_required;
+};
+
 struct tdx_sys_info {
 	struct tdx_sys_info_version version;
 	struct tdx_sys_info_features features;
 	struct tdx_sys_info_tdmr tdmr;
 	struct tdx_sys_info_td_ctrl td_ctrl;
 	struct tdx_sys_info_td_conf td_conf;
+	struct tdx_sys_info_ext ext;
 };
 
 #endif
diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 66b43350c6c3..a0c370894c0b 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -1175,6 +1175,30 @@ static __init int init_tdmrs(struct tdmr_info_list *tdmr_list)
 	return 0;
 }
 
+static __init int init_tdx_module_extensions(void)
+{
+	int ret;
+
+	if (!(tdx_sysinfo.features.tdx_features0 & TDX_FEATURES0_EXT))
+		return 0;
+
+	ret = get_tdx_sys_info_ext(&tdx_sysinfo.ext);
+	if (ret)
+		return ret;
+
+	/*
+	 * ext_required indicates if any add-on features requiring TDX module
+	 * extensions are configured via TDH.SYS.CONFIG. If none, skip the
+	 * initialization.
+	 */
+	if (!tdx_sysinfo.ext.ext_required)
+		return 0;
+
+	/* TODO: add the extensions enabling steps here */
+
+	return 0;
+}
+
 static __init int init_tdx_module(void)
 {
 	int ret;
@@ -1229,6 +1253,10 @@ static __init int init_tdx_module(void)
 	if (ret)
 		goto err_reset_pamts;
 
+	ret = init_tdx_module_extensions();
+	if (ret)
+		goto err_reset_pamts;
+
 	pr_info("%lu KB allocated for PAMT\n", tdmrs_count_pamt_kb(&tdx_tdmr_list));
 
 out_put_tdxmem:
diff --git a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
index e49c300f23d4..b9e1c011a990 100644
--- a/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
+++ b/arch/x86/virt/vmx/tdx/tdx_global_metadata.c
@@ -131,3 +131,17 @@ static __init int get_tdx_sys_info(struct tdx_sys_info *sysinfo)
 
 	return ret;
 }
+
+static __init int get_tdx_sys_info_ext(struct tdx_sys_info_ext *sysinfo_ext)
+{
+	int ret;
+	u64 val;
+
+	ret = read_sys_metadata_field(0x3100000000000001, &val);
+	if (ret)
+		return ret;
+
+	sysinfo_ext->ext_required = val;
+
+	return 0;
+}
-- 
2.25.1