linux-kernel - Re: [RFC PATCH v4 03/28] x86: Add the Secure Memory Encryption CPU feature

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Message-ID: <a1a6a6d7-3aac-3138-1e75-6160f0427a6b@amd.com>
Date:   Thu, 16 Feb 2017 13:42:13 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <linux-arch@...r.kernel.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <linux-doc@...r.kernel.org>,
        <x86@...nel.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>,
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        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
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        Brijesh Singh <brijesh.singh@....com>,
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        Thomas Gleixner <tglx@...utronix.de>,
        Larry Woodman <lwoodman@...hat.com>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v4 03/28] x86: Add the Secure Memory Encryption CPU
 feature

On 02/16/2017 12:13 PM, Borislav Petkov wrote:
> On Thu, Feb 16, 2017 at 09:42:36AM -0600, Tom Lendacky wrote:
>> Update the CPU features to include identifying and reporting on the
>> Secure Memory Encryption (SME) feature.  SME is identified by CPUID
>> 0x8000001f, but requires BIOS support to enable it (set bit 23 of
>> SYS_CFG MSR).  Only show the SME feature as available if reported by
>> CPUID and enabled by BIOS.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>> ---
>>  arch/x86/include/asm/cpufeature.h        |    7 +++++--
>>  arch/x86/include/asm/cpufeatures.h       |    5 ++++-
>>  arch/x86/include/asm/disabled-features.h |    3 ++-
>>  arch/x86/include/asm/msr-index.h         |    2 ++
>>  arch/x86/include/asm/required-features.h |    3 ++-
>>  arch/x86/kernel/cpu/common.c             |   19 +++++++++++++++++++
>>  6 files changed, 34 insertions(+), 5 deletions(-)
> 
> What happened here?
> 
> You had it already:
> 
> https://lkml.kernel.org/r/20161110003459.3280.25796.stgit@tlendack-t1.amdoffice.net
> 
> The bit in get_cpu_cap() with checking the MSR you can add at the end of
> init_amd() for example.

I realize it's a bit more code and expands the changes but I thought it
would be a bit clearer as to what was going on this way. And then the
follow on patch for the physical address reduction goes in nicely, too.

If you prefer I stay with the scattered feature approach and then clear
the bit based on the MSR at the end of init_amd() I can do that. I'm
not attached to either method.

Thanks,
Tom

>