Re: [PATCH v2] x86/cpu: Skip reading MSR_IA32_PLATFORM_ID in virtualized environment

[Binbin Wu]

On 5/11/2026 6:04 PM, Borislav Petkov wrote:
> On Thu, Apr 30, 2026 at 10:09:53AM +0800, Binbin Wu wrote:
>> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
>> index 37ac4afe0972..1bc0c350726c 100644
>> --- a/arch/x86/kernel/cpu/microcode/intel.c
>> +++ b/arch/x86/kernel/cpu/microcode/intel.c
>> @@ -147,6 +147,10 @@ u32 intel_get_platform_id(void)
>>  	if (intel_cpuid_vfm() <= INTEL_PENTIUM_II_KLAMATH)
>>  		return 0;
>>  
>> +	/* Don't try to read microcode bits when virtualized. */
>> +	if (cpuid_ecx(1) & BIT(X86_FEATURE_HYPERVISOR & 0x1f))
>> +		return 0;
>> +
>>  	/* get processor flags from MSR 0x17 */
>>  	native_rdmsr(MSR_IA32_PLATFORM_ID, val[0], val[1]);
>>  
>>
>> base-commit: 9974969c14031a097d6b45bcb7a06bb4aa525c40
>> -- 
> 
> Does that work too?
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index 18d2eff7a4b7..1b24de94bdd5 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -139,6 +139,9 @@ u32 intel_get_platform_id(void)
>  {
>  	unsigned int val[2];
>  
> +	if (hypervisor_present)

hypervisor_present could be uninitialized if dis_ucode_ldr is true.
intel_get_platform_id() is also called during the normal cpu initialization.


> +		return 0;
> +
>  	/*
>  	 * This can be called early. Use CPUID directly instead of
>  	 * relying on cpuinfo_x86 which may not be fully initialized.
>