Date: Tue, 11 Jul 2017 07:56:59 +0200
From: Borislav Petkov <bp@alien8.de>
To: Brian Gerst <brgerst@gmail.com>,
        Tom Lendacky <thomas.lendacky@amd.com>
Cc: linux-arch <linux-arch@vger.kernel.org>, linux-efi@vger.kernel.org,
        kvm@vger.kernel.org, linux-doc@vger.kernel.org,
        the arch/x86 maintainers <x86@kernel.org>, kexec@lists.infradead.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        kasan-dev@googlegroups.com, xen-devel@lists.xen.org,
        Linux-MM <linux-mm@kvack.org>, iommu@lists.linux-foundation.org,
        Brijesh Singh <brijesh.singh@amd.com>,
        Toshimitsu Kani <toshi.kani@hpe.com>,
        Radim =?utf-8?B?S3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Matt Fleming <matt@codeblueprint.co.uk>,
        Alexander Potapenko <glider@google.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Larry Woodman <lwoodman@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>, Joerg Roedel <joro@8bytes.org>,
        "Michael S. Tsirkin" <mst@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Dave Young <dyoung@redhat.com>, Rik van Riel <riel@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
        Andy Lutomirski <luto@kernel.org>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        Dmitry Vyukov <dvyukov@google.com>, Juergen Gross <jgross@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH v9 04/38] x86/CPU/AMD: Add the Secure Memory Encryption
 CPU feature
Message-ID: <20170711055659.GA4554@nazgul.tnic>
References: <20170707133804.29711.1616.stgit@tlendack-t1.amdoffice.net>
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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.
--