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

Tom Lendacky <thomas.lendacky@xxxxxxx> · Tue, 11 Jul 2017 10:14:34 -0500

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.