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- We made the FRED support an opt-in initially out of fear of it breaking

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machines left and right in the case of a hw bug in the first generation of
   machines supporting it. Now that that the FRED code has seen a lot of
   hammering, flip the logic to be opt-out as is the usual case with new hw
   features
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Merge tag 'x86_fred_for_v7.1_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 FRED updates from Borislav Petkov:
 "We made the FRED support an opt-in initially out of fear of it
  breaking machines left and right in the case of a hw bug in the first
  generation of machines supporting it.

  Now that that the FRED code has seen a lot of hammering, flip the
  logic to be opt-out as is the usual case with new hw features"

* tag 'x86_fred_for_v7.1_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/fred: Remove kernel log message when initializing exceptions
  x86/fred: Enable FRED by default
This commit is contained in:
Linus Torvalds 2026-04-14 14:50:51 -07:00
commit e9635f2a73
4 changed files with 4 additions and 7 deletions
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4
Documentation/admin-guide/kernel-parameters.txt
View File

@ -1765,8 +1765,8 @@ 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

2
arch/x86/Kconfig
View File

@ -554,7 +554,7 @@ 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.

2
arch/x86/kernel/cpu/common.c
View File

@ -1761,7 +1761,7 @@ 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));

3
arch/x86/kernel/fred.c
View File

@ -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