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

From: Tom Lendacky
Date: Tue Jul 11 2017 - 11:15:01 EST

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

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);
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.