linux-kernel - Re: [RFC, PATCHv1 15/28] x86: detect 5-level paging support

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Message-ID: <CA+55aFzgp+6c6RhgYvEjor=_+ewMeYL4XY4BqER5HMUknXBDCA@mail.gmail.com>
Date:   Thu, 8 Dec 2016 12:08:53 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Andy Lutomirski <luto@...capital.net>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC, PATCHv1 15/28] x86: detect 5-level paging support

On Thu, Dec 8, 2016 at 12:05 PM, Borislav Petkov <bp@...en8.de> wrote:
>
> The cpuid() in cpuflags.c doesn't zero ecx which, if we have to be
> pedantic, it should do. It calls CPUID now with the ptr value of its 4th
> on 64-bit and 3rd arg on 32-bit, respectively, IINM.

In fact, just do a single cpuid_count(), and then implement the
traditional cpuid() as just

   #define cpuid(x, a,b,c,d) cpuid_count(x, 0, a, b, c, d)

or something.

Especially since that's some of the ugliest inline asm ever due to the
nasty BX handling.

          Linus