On January 6, 2023 12:56:17 AM PST, Xin Li <xin3.li@xxxxxxxxx> wrote: >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@xxxxxxxxx> >--- > 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 Specifically, the intent is to enable it by default once hardware is widely available. This allows e.g. distros to compile in the support for opt-in field testing before throwing the switch. The motivation for this comes from the SMAP experience where the code was functional and correct when merged, but a change elsewhere in the kernel code base broke it during the intervening period.
