From: Dave Hansen Date: Wed, 4 Mar 2026 18:10:22 +0000 (-0800) Subject: x86/cpu: Add platform ID to CPU matching structure X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=fab0c75d500fd23de6ea1b30e44635418a6dae65;p=thirdparty%2Fkernel%2Flinux.git x86/cpu: Add platform ID to CPU matching structure The existing x86_match_cpu() infrastructure can be used to match a bunch of attributes of a CPU: vendor, family, model, steppings and CPU features. But, there's one more attribute that's missing and unable to be matched against: the platform ID, enumerated on Intel CPUs in MSR_IA32_PLATFORM_ID. It is a little more obscure and is only queried during microcode loading. This is because Intel sometimes has CPUs with identical family/model/stepping but which need different microcode. These CPUs are differentiated with the platform ID. Add a field in 'struct x86_cpu_id' for the platform ID. Similar to the stepping field, make the new field a mask of platform IDs. Some examples: 0x01: matches only platform ID 0x0 0x02: matches only platform ID 0x1 0x03: matches platform IDs 0x0 or 0x1 0x80: matches only platform ID 0x7 0xff: matches all 8 possible platform IDs Since the mask is only a byte wide, it nestles in next to another u8 and does not even increase the size of 'struct x86_cpu_id'. Reserve the all 0's value as the wildcard (X86_PLATFORM_ANY). This avoids forcing changes to existing 'struct x86_cpu_id' users. They can just continue to fill the field with 0's and their matching will work exactly as before. Note: If someone is ever looking for space in 'struct x86_cpu_id', this new field could probably get stuck over in ->driver_data for the one user that there is. Signed-off-by: Dave Hansen Reviewed-by: Sohil Mehta Link: https://patch.msgid.link/20260304181022.058DF07C@davehans-spike.ostc.intel.com --- diff --git a/arch/x86/kernel/cpu/match.c b/arch/x86/kernel/cpu/match.c index 6af1e8baeb0f2..4604802692dae 100644 --- a/arch/x86/kernel/cpu/match.c +++ b/arch/x86/kernel/cpu/match.c @@ -76,6 +76,9 @@ const struct x86_cpu_id *x86_match_cpu(const struct x86_cpu_id *match) if (m->steppings != X86_STEPPING_ANY && !(BIT(c->x86_stepping) & m->steppings)) continue; + if (m->platform_mask != X86_PLATFORM_ANY && + !(BIT(c->intel_platform_id) & m->platform_mask)) + continue; if (m->feature != X86_FEATURE_ANY && !cpu_has(c, m->feature)) continue; if (!x86_match_vendor_cpu_type(c, m)) diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h index 5b1725fe97076..23ff24080dfd9 100644 --- a/include/linux/mod_devicetable.h +++ b/include/linux/mod_devicetable.h @@ -691,6 +691,7 @@ struct x86_cpu_id { __u16 feature; /* bit index */ /* Solely for kernel-internal use: DO NOT EXPORT to userspace! */ __u16 flags; + __u8 platform_mask; __u8 type; kernel_ulong_t driver_data; }; @@ -702,6 +703,7 @@ struct x86_cpu_id { #define X86_STEPPING_ANY 0 #define X86_STEP_MIN 0 #define X86_STEP_MAX 0xf +#define X86_PLATFORM_ANY 0x0 #define X86_FEATURE_ANY 0 /* Same as FPU, you can't test for that */ #define X86_CPU_TYPE_ANY 0