linux-kernel - Re: [PATCH v5 17/32] x86/mm: Add support to access boot related data in the clear

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Message-ID: <20170518090212.kebstmnjv4h3cjf2@pd.tnic>
Date:   Thu, 18 May 2017 11:02:12 +0200
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,
        kexec@...ts.infradead.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>,
        Toshimitsu Kani <toshi.kani@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Brijesh Singh <brijesh.singh@....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>,
        Dave Young <dyoung@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [PATCH v5 17/32] x86/mm: Add support to access boot related data
 in the clear

On Wed, May 17, 2017 at 01:54:39PM -0500, Tom Lendacky wrote:
> I was worried what the compiler might do when CONFIG_EFI is not set,
> but it appears to take care of it. I'll double check though.

There's a efi_enabled() !CONFIG_EFI version too, so should be fine.

> I may introduce a length variable to capture data->len right after
> paddr_next is set and then have just a single memunmap() call before
> the if check.

Yap.

> I tried that, but calling an "__init" function (early_memremap()) from
> a non "__init" function generated warnings. I suppose I can pass in a
> function for the map and unmap but that looks worse to me (also the
> unmap functions take different arguments).

No, the other way around: the __init function should call the non-init
one and you need the non-init one anyway for memremap_is_setup_data().

> This is like the chicken and the egg scenario. In order to determine if
> an address is setup data I have to explicitly map the setup data chain
> as decrypted. In order to do that I have to supply a flag to explicitly
> map the data decrypted otherwise I wind up back in the
> memremap_is_setup_data() function again and again and again...

Oh, fun.

-- 
Regards/Gruss,
    Boris.

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