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

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Message-ID: <20170420165922.j2inlwbchrs6senw@pd.tnic>
Date:   Thu, 20 Apr 2017 18:59:22 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-mm@...ck.org,
        iommu@...ts.linux-foundation.org, Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: 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@....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.

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