[RFC PATCH 20/21] x86/virt/tdx: Add kernel command line to opt-in TDX host support

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

Enabling TDX consumes additional memory (used by TDX as metadata) and
additional initialization time.  Introduce a kernel command line to
allow to opt-in TDX host kernel support when user truly wants to use
TDX.

Signed-off-by: Kai Huang <kai.huang@intel.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
 arch/x86/virt/vmx/tdx.c                         | 14 ++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index f5a27f067db9..9f85cafd0c2d 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5707,6 +5707,12 @@
 
 	tdfx=		[HW,DRM]
 
+	tdx_host=	[X86-64, TDX]
+			Format: {on|off}
+			on: Enable TDX host kernel support
+			off: Disable TDX host kernel support
+			Default is off.
+
 	test_suspend=	[SUSPEND][,N]
 			Specify "mem" (for Suspend-to-RAM) or "standby" (for
 			standby suspend) or "freeze" (for suspend type freeze)
diff --git a/arch/x86/virt/vmx/tdx.c b/arch/x86/virt/vmx/tdx.c
index f704fddc9dfc..60d58b2daabd 100644
--- a/arch/x86/virt/vmx/tdx.c
+++ b/arch/x86/virt/vmx/tdx.c
@@ -115,6 +115,16 @@ static struct tdsysinfo_struct tdx_sysinfo;
 /* TDX global KeyID to protect TDX metadata */
 static u32 tdx_global_keyid;
 
+static bool enable_tdx_host;
+
+static int __init tdx_host_setup(char *s)
+{
+	if (!strcmp(s, "on"))
+		enable_tdx_host = true;
+	return 0;
+}
+__setup("tdx_host=", tdx_host_setup);
+
 static bool __seamrr_enabled(void)
 {
 	return (seamrr_mask & SEAMRR_ENABLED_BITS) == SEAMRR_ENABLED_BITS;
@@ -501,6 +511,10 @@ static int detect_p_seamldr(void)
 
 static int __tdx_detect(void)
 {
+	/* Disabled by kernel command line */
+	if (!enable_tdx_host)
+		goto no_tdx_module;
+
 	/*
 	 * TDX module cannot be possibly loaded if SEAMRR is disabled.
 	 * Also do not report TDX module as loaded if there's no enough
-- 
2.33.1