linux-kernel - [PATCH 04/11] x86/acpi: Check MWAIT feature instead of CPUID level

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Message-Id: <20241030213318.55C19666@davehans-spike.ostc.intel.com>
Date: Wed, 30 Oct 2024 14:33:18 -0700
From: Dave Hansen <dave.hansen@...ux.intel.com>
To: linux-kernel@...r.kernel.org
Cc: x86@...nel.org,tglx@...utronix.de,bp@...en8.de,rafael@...nel.org,lenb@...nel.org,Dave Hansen <dave.hansen@...ux.intel.com>
Subject: [PATCH 04/11] x86/acpi: Check MWAIT feature instead of CPUID level


From: Dave Hansen <dave.hansen@...ux.intel.com>

I think this code is possibly buggy.  The CPU could have a high
c->cpuid_level and not support MWAIT at all.  It is much more clear to
just check for MWAIT support directly.  Also, because of the CPU level
dependency code, any CPU that has X86_FEATURE_MWAIT also has a
high-enough CPUID level.

Check X86_FEATURE_MWAIT instead of the CPUID level.

Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
---

 b/arch/x86/kernel/acpi/cstate.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff -puN arch/x86/kernel/acpi/cstate.c~mwait-leaf-checks-3 arch/x86/kernel/acpi/cstate.c
--- a/arch/x86/kernel/acpi/cstate.c~mwait-leaf-checks-3	2024-10-30 12:28:10.374352561 -0700
+++ b/arch/x86/kernel/acpi/cstate.c	2024-10-30 12:28:10.374352561 -0700
@@ -173,7 +173,7 @@ int acpi_processor_ffh_cstate_probe(unsi
 	struct cpuinfo_x86 *c = &cpu_data(cpu);
 	long retval;
 
-	if (!cpu_cstate_entry || c->cpuid_level < CPUID_MWAIT_LEAF)
+	if (!cpu_cstate_entry || cpu_has(c, X86_FEATURE_MWAIT))
 		return -1;
 
 	if (reg->bit_offset != NATIVE_CSTATE_BEYOND_HALT)
_