Re: [PATCH 4/4] x86/pti: Do not enable PTI on fixed Intel processors

[Thomas Gleixner <tglx@linutronix.de>]

On Sat, 20 Jan 2018, David Woodhouse wrote:

> When they advertise the IA32_ARCH_CAPABILITIES MSR and it has the RDCL_NO
> bit set, they don't need KPTI either.

Do they exist today? And do we have documentation for that new MSR already?

Thanks,

	tglx

> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
>  arch/x86/kernel/cpu/common.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
> index e5d66e9..80572ae 100644
> --- a/arch/x86/kernel/cpu/common.c
> +++ b/arch/x86/kernel/cpu/common.c
> @@ -900,8 +900,13 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c)
>  
>  	setup_force_cpu_cap(X86_FEATURE_ALWAYS);
>  
> -	if (c->x86_vendor != X86_VENDOR_AMD)
> -		setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
> +	if (c->x86_vendor != X86_VENDOR_AMD) {
> +		unsigned long ia32_cap = 0;
> +		if (cpu_has(c, X86_FEATURE_ARCH_CAPABILITIES))
> +			rdmsrl(MSR_IA32_ARCH_CAPABILITIES, ia32_cap);
> +		if (!(ia32_cap & ARCH_CAP_RDCL_NO))
> +			setup_force_cpu_bug(X86_BUG_CPU_MELTDOWN);
> +	}
>  
>  	setup_force_cpu_bug(X86_BUG_SPECTRE_V1);
>  	setup_force_cpu_bug(X86_BUG_SPECTRE_V2);
> -- 
> 2.7.4
> 
>