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Message-Id: <20220727161026.871390189@linuxfoundation.org>
Date: Wed, 27 Jul 2022 18:13:21 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-kernel@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
stable@...r.kernel.org,
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
"Peter Zijlstra (Intel)" <peterz@...radead.org>,
Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Subject: [PATCH 5.18 137/158] x86/bugs: Warn when "ibrs" mitigation is selected on Enhanced IBRS parts
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
commit eb23b5ef9131e6d65011de349a4d25ef1b3d4314 upstream.
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@...ux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Reviewed-by: Thadeu Lima de Souza Cascardo <cascardo@...onical.com>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/r/2a5eaf54583c2bfe0edc4fea64006656256cca17.1657814857.git.pawan.kumar.gupta@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
arch/x86/kernel/cpu/bugs.c | 3 +++
1 file changed, 3 insertions(+)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -968,6 +968,7 @@ static inline const char *spectre_v2_mod
#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)
@@ -1408,6 +1409,8 @@ static void __init spectre_v2_select_mit
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:
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