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Date: Sat, 27 May 2017 01:10:59 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Andi Kleen <ak@linux.intel.com>,
        Dave Hansen <dave.hansen@intel.com>,
        Andy Lutomirski <luto@amacapital.net>, linux-arch@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: KASAN vs. boot-time switching between 4- and 5-level paging
Message-ID: <20170526221059.o4kyt3ijdweurz6j@node.shutemov.name>
References: <20170525203334.867-1-kirill.shutemov@linux.intel.com>
 <20170525203334.867-8-kirill.shutemov@linux.intel.com>
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On Thu, May 25, 2017 at 11:33:33PM +0300, Kirill A. Shutemov wrote:
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 0bf81e837cbf..c795207d8a3c 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -100,7 +100,7 @@ config X86
>  	select HAVE_ARCH_AUDITSYSCALL
>  	select HAVE_ARCH_HUGE_VMAP		if X86_64 || X86_PAE
>  	select HAVE_ARCH_JUMP_LABEL
> -	select HAVE_ARCH_KASAN			if X86_64 && SPARSEMEM_VMEMMAP
> +	select HAVE_ARCH_KASAN			if X86_64 && SPARSEMEM_VMEMMAP && !X86_5LEVEL
>  	select HAVE_ARCH_KGDB
>  	select HAVE_ARCH_KMEMCHECK
>  	select HAVE_ARCH_MMAP_RND_BITS		if MMU

Looks like KASAN will be a problem for boot-time paging mode switching.
It wants to know CONFIG_KASAN_SHADOW_OFFSET at compile-time to pass to
gcc -fasan-shadow-offset=. But this value varies between paging modes...

I don't see how to solve it. Folks, any ideas?

-- 
 Kirill A. Shutemov