linux-kernel - [PATCH v3 20/21] x86/virt/tdx: Add kernel command line to opt-in TDX host support

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Date:   Wed,  6 Apr 2022 16:49:32 +1200
From:   Kai Huang <kai.huang@...el.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, dave.hansen@...el.com,
        len.brown@...el.com, tony.luck@...el.com,
        rafael.j.wysocki@...el.com, reinette.chatre@...el.com,
        dan.j.williams@...el.com, peterz@...radead.org, ak@...ux.intel.com,
        kirill.shutemov@...ux.intel.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        isaku.yamahata@...el.com, kai.huang@...el.com
Subject: [PATCH v3 20/21] x86/virt/tdx: Add kernel command line to opt-in TDX host support

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@...el.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  6 ++++++
 arch/x86/virt/vmx/tdx/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 3f1cc5e317ed..cfa5b36890ea 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5790,6 +5790,12 @@
 
 	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/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 031af7b83cea..fee243cd454f 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -116,6 +116,16 @@ 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 1;
+}
+__setup("tdx_host=", tdx_host_setup);
+
 static bool __seamrr_enabled(void)
 {
 	return (seamrr_mask & SEAMRR_ENABLED_BITS) == SEAMRR_ENABLED_BITS;
@@ -500,6 +510,10 @@ static int detect_p_seamldr(void)
 
 static int __tdx_detect(void)
 {
+	/* Disabled by kernel command line */
+	if (!enable_tdx_host)
+		goto no_tdx_module;
+
 	/* The TDX module is not loaded if SEAMRR is disabled */
 	if (!seamrr_enabled()) {
 		pr_info("SEAMRR not enabled.\n");
-- 
2.35.1