linux-kernel - Re: [RFC PATCH v3 11/20] x86: Add support for changing memory encryption attribute

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Date:   Mon, 21 Nov 2016 09:27:54 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
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>,
        Joerg Roedel <joro@...tes.org>,
        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 11/20] x86: Add support for changing memory
 encryption attribute

On Sat, Nov 19, 2016 at 12:48:27PM -0600, Tom Lendacky wrote:
> Should I move this functionality into the sme_set_mem_* functions or
> remove the sme_set_mem_* functions and use the set_memory_* functions
> directly.  The latter means calculating the number of pages, but makes
> it clear that this works on a page level while the former keeps
> everything the mem_encrypt.c file (and I can change that to take in a
> page count so that it is clear about the page boundary usage).

A user of that interface doesn't care, right?

All she wants to do is pass in an address and size and the code will
figure out everything. And I think address and size is the simplest two
args you can pass. numpages can be calculated from it. As you do in
sme_set_mem_*.

And you need to do it all in pageattr.c because it uses the cpa wankery
in there so you probably want to define

int set_memory_dec(unsigned long addr, size_t size)
int set_memory_enc(unsigned long addr, size_t size)

there which both simply call

__set_memory_enc_dec(unsigned long addr, size_t size, bool enc)

and it goes and figures out everything, builds the cpa_data and does the
mapping.

That looks very simple and clean to me.

-- 
Regards/Gruss,
    Boris.

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