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authorLinus Torvalds <torvalds@linux-foundation.org>2022-08-01 19:49:29 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2022-08-01 19:49:29 +0300
commit42efa5e3a8888c45c15fc5a567cd77049a2e30f1 (patch)
treeb72f6bf5e213d60615b3e54fac9757127d0d665c /arch/x86/kernel/process.c
parent650ea1f626ab4d939fda00b7cca57698dcf57e5e (diff)
parent3f2adf00f52b5f2e9e9f23bb5c77608fc9ee297c (diff)
downloadlinux-42efa5e3a8888c45c15fc5a567cd77049a2e30f1.tar.xz
Merge tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 cpu updates from Borislav Petkov: - Remove the vendor check when selecting MWAIT as the default idle state - Respect idle=nomwait when supplied on the kernel cmdline - Two small cleanups * tag 'x86_cpu_for_v6.0_rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/cpu: Use MSR_IA32_MISC_ENABLE constants x86: Fix comment for X86_FEATURE_ZEN x86: Remove vendor checks from prefer_mwait_c1_over_halt x86: Handle idle=nomwait cmdline properly for x86_idle
Diffstat (limited to 'arch/x86/kernel/process.c')
-rw-r--r--arch/x86/kernel/process.c44
1 files changed, 31 insertions, 13 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index d456ce21c255..58a6ea472db9 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -810,24 +810,43 @@ static void amd_e400_idle(void)
}
/*
- * Intel Core2 and older machines prefer MWAIT over HALT for C1.
- * We can't rely on cpuidle installing MWAIT, because it will not load
- * on systems that support only C1 -- so the boot default must be MWAIT.
+ * Prefer MWAIT over HALT if MWAIT is supported, MWAIT_CPUID leaf
+ * exists and whenever MONITOR/MWAIT extensions are present there is at
+ * least one C1 substate.
*
- * Some AMD machines are the opposite, they depend on using HALT.
- *
- * So for default C1, which is used during boot until cpuidle loads,
- * use MWAIT-C1 on Intel HW that has it, else use HALT.
+ * Do not prefer MWAIT if MONITOR instruction has a bug or idle=nomwait
+ * is passed to kernel commandline parameter.
*/
static int prefer_mwait_c1_over_halt(const struct cpuinfo_x86 *c)
{
- if (c->x86_vendor != X86_VENDOR_INTEL)
+ u32 eax, ebx, ecx, edx;
+
+ /* User has disallowed the use of MWAIT. Fallback to HALT */
+ if (boot_option_idle_override == IDLE_NOMWAIT)
return 0;
- if (!cpu_has(c, X86_FEATURE_MWAIT) || boot_cpu_has_bug(X86_BUG_MONITOR))
+ /* MWAIT is not supported on this platform. Fallback to HALT */
+ if (!cpu_has(c, X86_FEATURE_MWAIT))
return 0;
- return 1;
+ /* Monitor has a bug. Fallback to HALT */
+ if (boot_cpu_has_bug(X86_BUG_MONITOR))
+ return 0;
+
+ cpuid(CPUID_MWAIT_LEAF, &eax, &ebx, &ecx, &edx);
+
+ /*
+ * If MWAIT extensions are not available, it is safe to use MWAIT
+ * with EAX=0, ECX=0.
+ */
+ if (!(ecx & CPUID5_ECX_EXTENSIONS_SUPPORTED))
+ return 1;
+
+ /*
+ * If MWAIT extensions are available, there should be at least one
+ * MWAIT C1 substate present.
+ */
+ return (edx & MWAIT_C1_SUBSTATE_MASK);
}
/*
@@ -932,9 +951,8 @@ static int __init idle_setup(char *str)
} else if (!strcmp(str, "nomwait")) {
/*
* If the boot option of "idle=nomwait" is added,
- * it means that mwait will be disabled for CPU C2/C3
- * states. In such case it won't touch the variable
- * of boot_option_idle_override.
+ * it means that mwait will be disabled for CPU C1/C2/C3
+ * states.
*/
boot_option_idle_override = IDLE_NOMWAIT;
} else