Re: Old microcode CPU matching issue - x86/microcode/intel: Refresh the revisions that determine old_microcode

[Jon Kohler]

> On Nov 20, 2025, at 7:39 PM, Dave Hansen <dave.hansen@xxxxxxxxx> wrote:
> 
> On 11/20/25 11:27, Dave Hansen wrote:
>> On 11/20/25 11:13, Sohil Mehta wrote:
>>> The early loading probably gets affected because intel_get_platform_id()
>>> relies on boot_cpu_data which isn't initialized when load_ucode_bsp() is
>>> called very early.
>> Good point, and thanks for finding those bugs!
>> 
>> We can probably just move back to building the vfm value from CPUID
>> directly as opposed to reading it from boot_cpu_data.
> 
> OK, here's a theoretically fixed up series. I actually booted this on
> real hardware and made sure I didn't break microcode loading in general:
> 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__git.kernel.org_pub_scm_linux_kernel_git_daveh_devel.git_log_-3Fh-3Dold-2Ducode-2Dplatform&d=DwICaQ&c=s883GpUCOChKOHiocYtGcg&r=NGPRGGo37mQiSXgHKm5rCQ&m=Aj3XdJqTpjECR_fyNML3SeMNT46oTwjdjYY5YqPSZ0k2Er9zbK7KbRrCX3jepXXq&s=XwRvvtN9Ch3mUF4-T-_lRIJBcpDpHgt5ebg5Hgl8ylg&e= 
> The actual hardware I tested on was this one:
> 
> { .flags = X86_CPU_ID_FLAG_ENTRY_VALID, .vendor = X86_VENDOR_INTEL, .family = 0x6,  .model = 0x7a, .steppings = 0x0002, .platform_mask = 0x01, .driver_data = 0x42 },
> 
> For testing, I added a 100% made up but matching CPU
> model/family/stepping that has (made up) later microcode and a
> (made up) higher platform ID that I added to the ucode-defs.h file:
> 
> { .flags = X86_CPU_ID_FLAG_ENTRY_VALID, .vendor = X86_VENDOR_INTEL, .family = 0x6,  .model = 0x7a, .steppings = 0x0002, .platform_mask = 0x02, .driver_data = 0x43 },
> 
> Everything seemed to work OK for me in my limited but nonzero
> amount of testing.
> 
> Any additional testing or eyeballs on the code would be appreciated.
> I'll post it for real in a day or two if it all looks OK.

Looks like it works, no longer complains of old microcode, loading works

Tested with 6.18 rc6 + our internal patch queue + your latest patches

Before, it was broken as reported before. After, works good.

[    2.451421] smpboot: CPU0: Intel(R) Xeon(R) Gold 5416S (family: 0x6, model: 0x8f, stepping: 0x8)
[    3.503508] microcode: Current revision: 0x2b000643
[    3.503510] microcode: Updated early from: 0x2b000620

tested-by/reported-by Jon Kohler <jon@xxxxxxxxxxx <mailto:jon@xxxxxxxxxxx>>

Thanks for tackling this!

Cheers,
Jon