Re: [Xen-devel] [PATCH v9 04/38] x86/CPU/AMD: Add the Secure Memory Encryption CPU feature

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

On 7/11/2017 12:56 AM, Borislav Petkov wrote:
> On Tue, Jul 11, 2017 at 01:07:46AM -0400, Brian Gerst wrote:
> > > If I make the scattered feature support conditional on CONFIG_X86_64
> > > (based on comment below) then cpu_has() will always be false unless
> > > CONFIG_X86_64 is enabled. So this won't need to be wrapped by the
> > > #ifdef.
> > If you change it to use cpu_feature_enabled(), gcc will see that it is
> > disabled and eliminate the dead code at compile time.
> Just do this:
>
>         if (cpu_has(c, X86_FEATURE_SME)) {
>                if (IS_ENABLED(CONFIG_X86_32)) {
>                         clear_cpu_cap(c, X86_FEATURE_SME);
>                } else {
>                        u64 msr;
>
>                        /* Check if SME is enabled */
>                       rdmsrl(MSR_K8_SYSCFG, msr);
>                       if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
>                               clear_cpu_cap(c, X86_FEATURE_SME);
>                }
>         }
>
> so that it is explicit that we disable it on 32-bit and we can save us
> the ifdeffery elsewhere.
I'll use this method for the change and avoid the #ifdefs.

Thanks,
Tom

> Thanks.
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