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

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  Re: [PATCH v5 05/32] x86/CPU/AMD: Handle SME reduction in physical  address size Borislav Petkov <bp@alien8.de> - 2017-04-20 19:10 +0200
    Re: [PATCH v5 05/32] x86/CPU/AMD: Handle SME reduction in physical  address size Borislav Petkov <bp@alien8.de> - 2017-04-20 21:10 +0200

#1627681 — Re: [PATCH v5 05/32] x86/CPU/AMD: Handle SME reduction in physical address size

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);
        }

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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#1627749

On Thu, Apr 20, 2017 at 12:29:20PM -0500, Tom Lendacky wrote:
> 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()) ...

Cool, even better! :)

-- 
Regards/Gruss,
    Boris.

Good mailing practices for 400: avoid top-posting and trim the reply.

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