tjh.dev / kernel
Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel os linux
1
fork

Configure Feed

Select the types of activity you want to include in your feed.

x86/microcode: Refactor platform ID enumeration into a helper

Today, the only code that cares about the platform ID is the microcode
update code itself. To facilitate storing the platform ID in a more
generic place and using it outside of the microcode update itself, put
the enumeration into a helper function. Mirror
intel_get_microcode_revision()'s naming and location.

But, moving away from intel_collect_cpu_info() means that the model
and family information in CPUID is not readily available. Just call
CPUID again.

Note that the microcode header is a mask of supported platform IDs.
Only stick the ID part in the helper. Leave the 1<<id part in the
microcode handling.

Also note that the PII is weird. It does not really have a platform
ID because it doesn't even have the MSR. Just consider it to be
platform ID 0. Instead of saying >=PII, say <=PII. The PII is the
real oddball here being the only CPU with Linux microcode updates
but no platform ID. It's worth calling it out by name.

This does subtly change the sig->pf for the PII though from 0x0
to 0x1. Make up for that by ignoring sig->pf when the microcode
update platform mask is 0x0.

[ dhansen: reflow comment for bpetkov ]

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Sohil Mehta <sohil.mehta@intel.com>
Reviewed-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Link: https://patch.msgid.link/20260304181018.EB6404F8@davehans-spike.ostc.intel.com

Dave Hansen 238be4ba 11439c46

+43 -11
+43 -11
arch/x86/kernel/cpu/microcode/intel.c
··· 120 120 return et->count * EXT_SIGNATURE_SIZE + EXT_HEADER_SIZE; 121 121 } 122 122 123 + 124 + /* 125 + * Use CPUID to generate a "vfm" value. Useful before cpuinfo_x86 126 + * structures are populated. 127 + */ 128 + static u32 intel_cpuid_vfm(void) 129 + { 130 + u32 eax = cpuid_eax(1); 131 + u32 fam = x86_family(eax); 132 + u32 model = x86_model(eax); 133 + 134 + return IFM(fam, model); 135 + } 136 + 137 + static u32 intel_get_platform_id(void) 138 + { 139 + unsigned int val[2]; 140 + 141 + /* 142 + * This can be called early. Use CPUID directly instead of 143 + * relying on cpuinfo_x86 which may not be fully initialized. 144 + * The PII does not have MSR_IA32_PLATFORM_ID. Everything 145 + * before _it_ has no microcode (for Linux at least). 146 + */ 147 + if (intel_cpuid_vfm() <= INTEL_PENTIUM_II_KLAMATH) 148 + return 0; 149 + 150 + /* get processor flags from MSR 0x17 */ 151 + native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]); 152 + 153 + return (val[1] >> 18) & 7; 154 + } 155 + 123 156 void intel_collect_cpu_info(struct cpu_signature *sig) 124 157 { 125 158 sig->sig = cpuid_eax(1); 126 - sig->pf = 0; 127 159 sig->rev = intel_get_microcode_revision(); 128 - 129 - if (IFM(x86_family(sig->sig), x86_model(sig->sig)) >= INTEL_PENTIUM_III_DESCHUTES) { 130 - unsigned int val[2]; 131 - 132 - /* get processor flags from MSR 0x17 */ 133 - native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]); 134 - sig->pf = 1 << ((val[1] >> 18) & 7); 135 - } 160 + sig->pf = 1 << intel_get_platform_id(); 136 161 } 137 162 EXPORT_SYMBOL_GPL(intel_collect_cpu_info); 138 163 ··· 167 142 if (s1->sig != sig2) 168 143 return false; 169 144 170 - /* Processor flags are either both 0 or they intersect. */ 171 - return ((!s1->pf && !pf2) || (s1->pf & pf2)); 145 + /* 146 + * Consider an empty mask to match everything. This 147 + * should only occur for one CPU model, the PII. 148 + */ 149 + if (!pf2) 150 + return true; 151 + 152 + /* Is the CPU's platform ID in the signature mask? */ 153 + return s1->pf & pf2; 172 154 } 173 155 174 156 bool intel_find_matching_signature(void *mc, struct cpu_signature *sig)