linux-kernel - [RFC PATCH 32/32] x86/fred: disable FRED by default in its early stage

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Message-Id: <20221220063658.19271-33-xin3.li@intel.com>
Date:   Mon, 19 Dec 2022 22:36:58 -0800
From:   Xin Li <xin3.li@...el.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, peterz@...radead.org,
        andrew.cooper3@...rix.com, seanjc@...gle.com, pbonzini@...hat.com,
        ravi.v.shankar@...el.com
Subject: [RFC PATCH 32/32] x86/fred: disable FRED by default in its early stage

Disable FRED by default in its early stage.

To enable FRED, a new kernel command line option "fred" needs to be added.

Signed-off-by: Xin Li <xin3.li@...el.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++++
 arch/x86/kernel/cpu/common.c                    | 3 +++
 2 files changed, 7 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 42af9ca0127e..0bc76d926dd4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1506,6 +1506,10 @@
 			Warning: use of this parameter will taint the kernel
 			and may cause unknown problems.
 
+	fred
+			Forcefully enable flexible return and event delivery,
+			which is otherwise disabled by default.
+
 	ftrace=[tracer]
 			[FTRACE] will set and start the specified tracer
 			as early as possible in order to facilitate early
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 5de68356fe62..1a160337ad41 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1434,6 +1434,9 @@ static void __init cpu_parse_early_param(void)
 	char *argptr = arg, *opt;
 	int arglen, taint = 0;
 
+	if (!cmdline_find_option_bool(boot_command_line, "fred"))
+		setup_clear_cpu_cap(X86_FEATURE_FRED);
+
 #ifdef CONFIG_X86_32
 	if (cmdline_find_option_bool(boot_command_line, "no387"))
 #ifdef CONFIG_MATH_EMULATION
-- 
2.34.1