linux-kernel - Re: [RFC PATCH v2 04/20] x86: Secure Memory Encryption (SME) support

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Message-ID: <CALCETrVoiM3bskfWrg4c8ttHr467Us9xdXuxw=T6Dkr0PFo18g@mail.gmail.com>
Date:   Tue, 30 Aug 2016 07:57:25 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     kasan-dev <kasan-dev@...glegroups.com>,
        "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        iommu@...ts.linux-foundation.org,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        Jonathan Corbet <corbet@....net>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Alexander Potapenko <glider@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Arnd Bergmann <arnd@...db.de>, Joerg Roedel <joro@...tes.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        "H. Peter Anvin" <hpa@...or.com>, X86 ML <x86@...nel.org>,
        kvm list <kvm@...r.kernel.org>
Subject: Re: [RFC PATCH v2 04/20] x86: Secure Memory Encryption (SME) support

On Aug 30, 2016 6:34 AM, "Tom Lendacky" <thomas.lendacky@....com> wrote:
>
> On 08/25/2016 08:04 AM, Thomas Gleixner wrote:
> > On Mon, 22 Aug 2016, Tom Lendacky wrote:
> >
> >> Provide support for Secure Memory Encryption (SME). This initial support
> >> defines the memory encryption mask as a variable for quick access and an
> >> accessor for retrieving the number of physical addressing bits lost if
> >> SME is enabled.
> >
> > What is the reason that this needs to live in assembly code?
>
> In later patches this code is expanded and deals with a lot of page
> table manipulation, cpuid/rdmsr instructions, etc. and so I thought it
> was best to do it this way.

None of that sounds like it needs to be in asm, though.

I, at least, have a strong preference for minimizing the amount of asm
in the low-level arch code.

--Andy