Re: [PATCH v5 05/32] x86/CPU/AMD: Handle SME reduction in physical address size

Tom Lendacky
2017-04-20T17:29:39Z

On 4/20/2017 11:59 AM, Borislav Petkov wrote:
> On Tue, Apr 18, 2017 at 04:17:11PM -0500, Tom Lendacky wrote:
>> When System Memory Encryption (SME) is enabled, the physical address
>> space is reduced. Adjust the x86_phys_bits value to reflect this
>> reduction.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>> arch/x86/kernel/cpu/amd.c | 14 +++++++++++---
>> 1 file changed, 11 insertions(+), 3 deletions(-)
>
> ...
>
>> @@ -622,8 +624,14 @@ static void early_init_amd(struct cpuinfo_x86 *c)
>>
>> /* Check if SME is enabled */
>> rdmsrl(MSR_K8_SYSCFG, msr);
>> - if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
>> + if (msr & MSR_K8_SYSCFG_MEM_ENCRYPT) {
>> + unsigned int ebx;
>> +
>> + ebx = cpuid_ebx(0x8000001f);
>> + c->x86_phys_bits -= (ebx >> 6) & 0x3f;
>> + } else {
>> clear_cpu_cap(c, X86_FEATURE_SME);
>> + }
>
> Lemme do some simplifying to save an indent level, get rid of local var
> ebx and kill some { }-brackets for a bit better readability:
>
> if (c->extended_cpuid_level >= 0x8000001f) {
> u64 msr;
>
> if (!cpu_has(c, X86_FEATURE_SME))
> return;
>
> /* Check if SME is enabled */
> rdmsrl(MSR_K8_SYSCFG, msr);
> if (msr & MSR_K8_SYSCFG_MEM_ENCRYPT)
> c->x86_phys_bits -= (cpuid_ebx(0x8000001f) >> 6) & 0x3f;
> else
> clear_cpu_cap(c, X86_FEATURE_SME);
> }
>

Hmmm... and actually if cpu_has(X86_FEATURE_SME) is true then it's a
given that extended_cpuid_level >= 0x8000001f. So this can be
simplified to just:

if (cpu_has(c, X86_FEATURE_SME)) {
... the rest of your suggestion (minus cpu_has()) ...
}

Thanks,
Tom