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References: <20181026122856.66224-1-kirill.shutemov@linux.intel.com> <20181026122856.66224-2-kirill.shutemov@linux.intel.com>
In-Reply-To: <20181026122856.66224-2-kirill.shutemov@linux.intel.com>
From: Andy Lutomirski <luto@kernel.org>
Date: Fri, 2 Nov 2018 14:07:44 -0700
Message-ID: <CALCETrXMA=4694sstXYWK1rSiHBAFbN=kPpB5PcG2uBpyxoF3g@mail.gmail.com>
Subject: Re: [PATCHv3 1/3] x86/mm: Move LDT remap out of KASLR region on
 5-level paging
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Sender: owner-linux-mm@kvack.org
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To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>, Dave Hansen <dave.hansen@linux.intel.com>, Andrew Lutomirski <luto@kernel.org>, Peter Zijlstra <peterz@infradead.org>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, Baoquan He <bhe@redhat.com>, Matthew Wilcox <willy@infradead.org>, X86 ML <x86@kernel.org>, Linux-MM <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>

On Fri, Oct 26, 2018 at 5:29 AM Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
>
> On 5-level paging LDT remap area is placed in the middle of
> KASLR randomization region and it can overlap with direct mapping,
> vmalloc or vmap area.
>
> Let's move LDT just before direct mapping which makes it safe for KASLR.
> This also allows us to unify layout between 4- and 5-level paging.
>
> We don't touch 4 pgd slot gap just before the direct mapping reserved
> for a hypervisor, but move direct mapping by one slot instead.
>
> The LDT mapping is per-mm, so we cannot move it into P4D page table next
> to CPU_ENTRY_AREA without complicating PGD table allocation for 5-level
> paging.

Reviewed-by: Andy Lutomirski <luto@kernel.org>

(assuming it passes tests with 4-level and 5-level.  my test setup is
current busted, and i'm bisecting it.)