Re: [PATCH] x86/cpu, x86/pti: Do not enable PTI on AMD processors

[Tom Lendacky]

On 12/27/2017 2:48 AM, Dave Hansen wrote:
> On 12/26/2017 09:43 PM, Tom Lendacky wrote:
>> --- a/arch/x86/kernel/cpu/common.c
>> +++ b/arch/x86/kernel/cpu/common.c
>> @@ -923,8 +923,8 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
>>  
>>  	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
>>  
>> -	/* Assume for now that ALL x86 CPUs are insecure */
>> -	setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
>> +	if (c->x86_vendor != X86_VENDOR_AMD)
>> +		setup_force_cpu_bug(X86_BUG_CPU_INSECURE);
> 
> Does this disable it in a way that it can be turned back on via the
> kernel command-line?
> 

Yes, specifying pti=on on the command line will turn kernel page table
isolation on regardless of this setting.

Thanks,
Tom

> This is a rather wide class of issues and I would rather not just
> hard-code it in a way that we say one vendor has never and will never be
> affected.
>