linux-kernel - Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for memory encryption

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Date:   Thu, 8 Sep 2016 15:55:51 +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,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        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>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v2 07/20] x86: Provide general kernel support for
 memory encryption

On Thu, Sep 08, 2016 at 08:26:27AM -0500, Tom Lendacky wrote:
> When does this value get initialized?  Since _PAGE_ENC is #defined to
> sme_me_mask, which is not set until the boot process begins, I'm afraid
> we'd end up using the initial value of sme_me_mask, which is zero.  Do
> I have that right?

Hmm, but then that would hold true for all the other defines where you
OR-in _PAGE_ENC, no?

In any case, the preprocessed source looks like this:

pmdval_t early_pmd_flags = (((((((pteval_t)(1)) << 0) | (((pteval_t)(1)) << 1) | (((pteval_t)(1)) << 6) | (((pteval_t)(1)) << 5) | (((pteval_t)(1)) << 8)) | (((pteval_t)(1)) << 63)) | (((pteval_t)(1)) << 7)) | sme_me_mask) & ~((((pteval_t)(1)) << 8) | (((pteval_t)(1)) << 63));

but the problem is later, when building:

arch/x86/kernel/head64.c:39:28: error: initializer element is not constant
 pmdval_t early_pmd_flags = (__PAGE_KERNEL_LARGE | _PAGE_ENC) & ~(_PAGE_GLOBAL | _PAGE_NX);
                            ^
scripts/Makefile.build:153: recipe for target 'arch/x86/kernel/head64.s' failed

so I guess not. :-\

Ok, then at least please put the early_pmd_flags init after
sme_early_init() along with a small comment explaning what happens.

Thanks.

-- 
Regards/Gruss,
    Boris.

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