linux-kernel - Re: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d

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Message-ID: <20210120114438.GD825@zn.tnic>
Date:   Wed, 20 Jan 2021 12:44:38 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Arvind Sankar <nivedita@...m.mit.edu>,
        Arnd Bergmann <arnd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, X86 ML <x86@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Arnd Bergmann <arnd@...db.de>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        platform-driver-x86@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] x86: efi: avoid BUILD_BUG_ON() for non-constant p4d_index

On Wed, Jan 20, 2021 at 10:33:43AM +0100, Ard Biesheuvel wrote:
> The churn doesn't seem to be worth it, tbh.
> 
> So could we get rid of the complexity here, and only build_bug() on
> the start address of the EFI region being outside the topmost p4d?
> That should make the PGD test redundant as well.

Yah, makes sense to me.

Thx.

-- 
Regards/Gruss,
    Boris.

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