linux-kernel - Re: [RFC PATCH v3 04/20] x86: Handle reduction in physical address size with SME

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Message-ID: <a4cc5b07-89e1-aaa0-1977-1de95883ba62@amd.com>
Date:   Tue, 15 Nov 2016 08:40:05 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>
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>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.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>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v3 04/20] x86: Handle reduction in physical address
 size with SME

On 11/15/2016 6:14 AM, Borislav Petkov wrote:
> On Tue, Nov 15, 2016 at 01:10:35PM +0100, Joerg Roedel wrote:
>> Maybe add a comment here why you can't use cpu_has (yet).
> 
> So that could be alleviated by moving this function *after*
> init_scattered_cpuid_features(). Then you can simply do *cpu_has().

Yes, I can move it after init_scattered_cpuid_features() and then use
the cpu_has() function.  I'll make sure to include a comment that the
function needs to be called after init_scattered_cpuid_features().

> 
> Also, I'm not sure why we're checking CPUID for the SME feature when we
> have sme_get_me_mask() et al which have been setup much earlier...
> 

The feature may be present and enabled even if it is not currently
active.  In other words, the SYS_CFG MSR bit could be set but we aren't
actually using encryption (sme_me_mask is 0).  As long as the SYS_CFG
MSR bit is set we need to take into account the physical reduction in
address space.

Thanks,
Tom