From ca582161f5900991e26240e17f30740a8f3b9f2b Mon Sep 17 00:00:00 2001 From: Breno Leitao Date: Mon, 28 Nov 2022 07:31:48 -0800 Subject: x86/bugs: Reset speculation control settings on init [ Upstream commit 0125acda7d76b943ca55811df40ed6ec0ecf670f ] Currently, x86_spec_ctrl_base is read at boot time and speculative bits are set if Kconfig items are enabled. For example, IBRS is enabled if CONFIG_CPU_IBRS_ENTRY is configured, etc. These MSR bits are not cleared if the mitigations are disabled. This is a problem when kexec-ing a kernel that has the mitigation disabled from a kernel that has the mitigation enabled. In this case, the MSR bits are not cleared during the new kernel boot. As a result, this might have some performance degradation that is hard to pinpoint. This problem does not happen if the machine is (hard) rebooted because the bit will be cleared by default. [ bp: Massage. ] Suggested-by: Pawan Gupta Signed-off-by: Breno Leitao Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20221128153148.1129350-1-leitao@debian.org Signed-off-by: Sasha Levin --- arch/x86/include/asm/msr-index.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h index 0bd07699dba3..847f3f5820d2 100644 --- a/arch/x86/include/asm/msr-index.h +++ b/arch/x86/include/asm/msr-index.h @@ -50,6 +50,10 @@ #define SPEC_CTRL_RRSBA_DIS_S_SHIFT 6 /* Disable RRSBA behavior */ #define SPEC_CTRL_RRSBA_DIS_S BIT(SPEC_CTRL_RRSBA_DIS_S_SHIFT) +/* A mask for bits which the kernel toggles when controlling mitigations */ +#define SPEC_CTRL_MITIGATIONS_MASK (SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD \ + | SPEC_CTRL_RRSBA_DIS_S) + #define MSR_IA32_PRED_CMD 0x00000049 /* Prediction Command */ #define PRED_CMD_IBPB BIT(0) /* Indirect Branch Prediction Barrier */ -- cgit v1.2.3