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

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Message-ID: <25496e6a-ddf0-231a-f83d-cdc2f61e6d96@amd.com>
Date:   Tue, 15 Nov 2016 16:01:45 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
CC:     Joerg Roedel <joro@...tes.org>, <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 3:33 PM, Borislav Petkov wrote:
> On Tue, Nov 15, 2016 at 03:22:45PM -0600, Tom Lendacky wrote:
>> Hmmm... I still need the ebx value from the CPUID instruction to
>> calculate the proper reduction in physical bits, so I'll still need
>> to make the CPUID call.
> 
>         if (c->extended_cpuid_level >= 0x8000001f) {
>                 cpuid(0x8000001f, &eax, &ebx, &ecx, &edx);
> 
> 		...
> 
> just like the rest of get_cpu_cap() :)

Right, which is what the code does now.  I was looking at switching
over to the cpu_has() function and eliminate the cpuid call, but I
still need the cpuid call for the ebx value.

Thanks,
Tom

>