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

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Message-ID: <20170711055659.GA4554@nazgul.tnic>
Date:   Tue, 11 Jul 2017 07:56:59 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Brian Gerst <brgerst@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch <linux-arch@...r.kernel.org>, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        the arch/x86 maintainers <x86@...nel.org>,
        kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        kasan-dev@...glegroups.com, xen-devel@...ts.xen.org,
        Linux-MM <linux-mm@...ck.org>, iommu@...ts.linux-foundation.org,
        Brijesh Singh <brijesh.singh@....com>,
        Toshimitsu Kani <toshi.kani@....com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Alexander Potapenko <glider@...gle.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Joerg Roedel <joro@...tes.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dave Young <dyoung@...hat.com>, Rik van Riel <riel@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v9 04/38] x86/CPU/AMD: Add the Secure Memory Encryption
 CPU feature

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.

Thanks.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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