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

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Date:   Fri, 19 May 2017 15:50:32 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...en8.de>
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 5/18/2017 4:02 AM, Borislav Petkov wrote:
> 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().
>

The "worker" function would be doing the loop through the setup data,
but since the setup data is mapped inside the loop I can't do the __init
calling the non-init function and still hope to consolidate the code.
Maybe I'm missing something here...

Thanks,
Tom

>> 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.
>