Currently spectre_v2=ibrs forces write to MSR_IA32_SPEC_CTRL at every entry and exit. On Enhanced IBRS parts setting MSR_IA32_SPEC_CTRL[IBRS] only once at bootup is sufficient. MSR write at every kernel entry/exit incur unnecessary penalty that can be avoided.
When Enhanced IBRS feature is present, switch from "ibrs" to "auto" mode so that appropriate mitigation is selected.
Fixes: 7c693f54c873 ("x86/speculation: Add spectre_v2=ibrs option to support Kernel IBRS") Cc: stable@vger.kernel.org # 5.10+ Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com --- arch/x86/kernel/cpu/bugs.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 0dd04713434b..7d7ebfdfbeda 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -1303,6 +1303,12 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) return SPECTRE_V2_CMD_AUTO; }
+ if (cmd == SPECTRE_V2_CMD_IBRS && boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) { + pr_err("%s selected but CPU supports Enhanced IBRS. Switching to AUTO select\n", + mitigation_options[i].option); + return SPECTRE_V2_CMD_AUTO; + } + spec_v2_print_cond(mitigation_options[i].option, mitigation_options[i].secure); return cmd;
base-commit: 72a8e05d4f66b5af7854df4490e3135168694b6b