The following commit has been merged into the x86/urgent branch of tip:
Commit-ID: eb23b5ef9131e6d65011de349a4d25ef1b3d4314 Gitweb: https://git.kernel.org/tip/eb23b5ef9131e6d65011de349a4d25ef1b3d4314 Author: Pawan Gupta pawan.kumar.gupta@linux.intel.com AuthorDate: Thu, 14 Jul 2022 16:15:35 -07:00 Committer: Peter Zijlstra peterz@infradead.org CommitterDate: Wed, 20 Jul 2022 19:24:53 +02:00
x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts
IBRS mitigation for spectre_v2 forces write to MSR_IA32_SPEC_CTRL at every kernel entry/exit. On Enhanced IBRS parts setting MSR_IA32_SPEC_CTRL[IBRS] only once at boot is sufficient. MSR writes at every kernel entry/exit incur unnecessary performance loss.
When Enhanced IBRS feature is present, print a warning about this unnecessary performance loss.
Signed-off-by: Pawan Gupta pawan.kumar.gupta@linux.intel.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Thadeu Lima de Souza Cascardo cascardo@canonical.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/2a5eaf54583c2bfe0edc4fea64006656256cca17.165781485... --- arch/x86/kernel/cpu/bugs.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index 78c9082..6454bc7 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -975,6 +975,7 @@ static inline const char *spectre_v2_module_string(void) { return ""; } #define SPECTRE_V2_LFENCE_MSG "WARNING: LFENCE mitigation is not recommended for this CPU, data leaks possible!\n" #define SPECTRE_V2_EIBRS_EBPF_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS on, data leaks possible via Spectre v2 BHB attacks!\n" #define SPECTRE_V2_EIBRS_LFENCE_EBPF_SMT_MSG "WARNING: Unprivileged eBPF is enabled with eIBRS+LFENCE mitigation and SMT, data leaks possible via Spectre v2 BHB attacks!\n" +#define SPECTRE_V2_IBRS_PERF_MSG "WARNING: IBRS mitigation selected on Enhanced IBRS CPU, this may cause unnecessary performance loss\n"
#ifdef CONFIG_BPF_SYSCALL void unpriv_ebpf_notify(int new_state) @@ -1415,6 +1416,8 @@ static void __init spectre_v2_select_mitigation(void)
case SPECTRE_V2_IBRS: setup_force_cpu_cap(X86_FEATURE_KERNEL_IBRS); + if (boot_cpu_has(X86_FEATURE_IBRS_ENHANCED)) + pr_warn(SPECTRE_V2_IBRS_PERF_MSG); break;
case SPECTRE_V2_LFENCE: