[PATCH v2 0/3] x86/fred: enable FRED by default

[H. Peter Anvin]

From: H. Peter Anvin (Intel) <hpa@xxxxxxxxx>

When FRED was added to the mainline kernel, it was set up as an
explicit opt-in due to the risk of regressions before hardware was
available publicly.

Now, Panther Lake (Core Ultra 300 series) has been released, and
benchmarking by Phoronix has shown that it provides a significant
performance benefit on most workloads:

    https://www.phoronix.com/review/intel-fred-panther-lake

Accordingly, enable FRED by default if the CPU supports it. FRED can
of course still be disabled via the fred=off command line option.

Changes in v2:

- Ignore fred= options other than fred={on,off}. In practice
  of course this means options other than fred=off.
- Remove FRED initialization message during CPU bringup (Sohil Mehta)

---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++--
 arch/x86/Kconfig                                | 2 +-
 arch/x86/kernel/cpu/common.c                    | 2 +-
 arch/x86/kernel/fred.c                          | 3 ---
 4 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 03a550630644..bfa8a20ccc37 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1750,8 +1750,8 @@ Kernel parameters
 	fred=		[X86-64]
 			Enable/disable Flexible Return and Event Delivery.
 			Format: { on | off }
-			on: enable FRED when it's present.
-			off: disable FRED, the default setting.
+			on: enable FRED when it's present, the default setting.
+			off: disable FRED.
 
 	ftrace=[tracer]
 			[FTRACE] will set and start the specified tracer
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index e2df1b147184..876b663dcf38 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -557,7 +557,7 @@ config X86_FRED
 	bool "Flexible Return and Event Delivery"
 	depends on X86_64
 	help
-	  When enabled, try to use Flexible Return and Event Delivery
+	  When enabled, use Flexible Return and Event Delivery
 	  instead of the legacy SYSCALL/SYSENTER/IDT architecture for
 	  ring transitions and exception/interrupt handling if the
 	  system supports it.
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index a8ff4376c286..0b02cb038d7f 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1746,7 +1746,7 @@ static void __init cpu_parse_early_param(void)
 
 	/* Minimize the gap between FRED is available and available but disabled. */
 	arglen = cmdline_find_option(boot_command_line, "fred", arg, sizeof(arg));
-	if (arglen != 2 || strncmp(arg, "on", 2))
+	if (arglen == 3 && !strncmp(arg, "off", 3))
 		setup_clear_cpu_cap(X86_FEATURE_FRED);
 
 	arglen = cmdline_find_option(boot_command_line, "clearcpuid", arg, sizeof(arg));
diff --git a/arch/x86/kernel/fred.c b/arch/x86/kernel/fred.c
index e736b19e18de..117aa06d25ca 100644
--- a/arch/x86/kernel/fred.c
+++ b/arch/x86/kernel/fred.c
@@ -27,9 +27,6 @@ EXPORT_PER_CPU_SYMBOL(fred_rsp0);
 
 void cpu_init_fred_exceptions(void)
 {
-	/* When FRED is enabled by default, remove this log message */
-	pr_info("Initialize FRED on CPU%d\n", smp_processor_id());
-
 	/*
 	 * If a kernel event is delivered before a CPU goes to user level for
 	 * the first time, its SS is NULL thus NULL is pushed into the SS field