From: Dave Hansen dave.hansen@linux.intel.com
Andrew Cooper reported some boot issues on Ice Lake servers when running Xen that he tracked down to MWAIT not waking up. Do the safe thing and consider them buggy since there's a published erratum. Note: I've seen no reports of this occurring on Linux.
Add Ice Lake servers to the list of shaky MONITOR implementations with no workaround available. Also, before the if() gets too unwieldy, move it over to a x86_cpu_id array. Additionally, add a comment to the X86_BUG_MONITOR consumption site to make it clear how and why affected CPUs get IPIs to wake them up.
There is no equivalent erratum for the "Xeon D" Ice Lakes so INTEL_ICELAKE_D is not affected.
The erratum is called ICX143 in the "3rd Gen Intel Xeon Scalable Processors, Codename Ice Lake Specification Update". It is Intel document 637780, currently available here:
https://cdrdv2.intel.com/v1/dl/getContent/637780
Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Cc: Andrew Cooper andrew.cooper3@citrix.com Cc: Rafael J. Wysocki rafael.j.wysocki@intel.com Cc: Len Brown len.brown@intel.com Cc: Srinivas Pandruvada srinivas.pandruvada@linux.intel.com Cc: Peter Zijlstra peterz@infradead.org Cc: stable@vger.kernel.org
---
b/arch/x86/include/asm/mwait.h | 3 +++ b/arch/x86/kernel/cpu/intel.c | 17 ++++++++++++++--- 2 files changed, 17 insertions(+), 3 deletions(-)
diff -puN arch/x86/kernel/cpu/intel.c~ICX-MONITOR-bug arch/x86/kernel/cpu/intel.c --- a/arch/x86/kernel/cpu/intel.c~ICX-MONITOR-bug 2025-04-18 13:54:46.022590596 -0700 +++ b/arch/x86/kernel/cpu/intel.c 2025-04-18 15:15:19.374365069 -0700 @@ -513,6 +513,19 @@ static void init_intel_misc_features(str }
/* + * These CPUs have buggy MWAIT/MONITOR implementations that + * usually manifest as hangs or stalls at boot. + */ +#define MWAIT_VFM(_vfm) \ + X86_MATCH_VFM_FEATURE(_vfm, X86_FEATURE_MWAIT, 0) +static const struct x86_cpu_id monitor_bug_list[] = { + MWAIT_VFM(INTEL_ATOM_GOLDMONT), + MWAIT_VFM(INTEL_LUNARLAKE_M), + MWAIT_VFM(INTEL_ICELAKE_X), /* Erratum ICX143 */ + {}, +}; + +/* * This is a list of Intel CPUs that are known to suffer from downclocking when * ZMM registers (512-bit vectors) are used. On these CPUs, when the kernel * executes SIMD-optimized code such as cryptography functions or CRCs, it @@ -565,9 +578,7 @@ static void init_intel(struct cpuinfo_x8 c->x86_vfm == INTEL_WESTMERE_EX)) set_cpu_bug(c, X86_BUG_CLFLUSH_MONITOR);
- if (boot_cpu_has(X86_FEATURE_MWAIT) && - (c->x86_vfm == INTEL_ATOM_GOLDMONT || - c->x86_vfm == INTEL_LUNARLAKE_M)) + if (x86_match_cpu(monitor_bug_list)) set_cpu_bug(c, X86_BUG_MONITOR);
#ifdef CONFIG_X86_64 diff -puN arch/x86/include/asm/mwait.h~ICX-MONITOR-bug arch/x86/include/asm/mwait.h --- a/arch/x86/include/asm/mwait.h~ICX-MONITOR-bug 2025-04-18 15:17:18.353749634 -0700 +++ b/arch/x86/include/asm/mwait.h 2025-04-18 15:20:06.037927656 -0700 @@ -110,6 +110,9 @@ static __always_inline void __sti_mwait( * through MWAIT. Whenever someone changes need_resched, we would be woken * up from MWAIT (without an IPI). * + * Buggy (X86_BUG_MONITOR) CPUs will never set the polling bit and will + * always be sent IPIs. + * * New with Core Duo processors, MWAIT can take some hints based on CPU * capability. */ _