linux-kernel - Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging

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Message-ID: <B4C5A54B-FC84-4B73-8ECC-CD14532CBA2C@zytor.com>
Date:   Fri, 26 May 2017 12:36:31 -0700
From:   hpa@...or.com
To:     Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill@...temov.name>
CC:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging

On May 26, 2017 12:23:18 PM PDT, Dave Hansen <dave.hansen@...el.com> wrote:
>On 05/26/2017 11:24 AM, hpa@...or.com wrote:
>> The only case where that even has any utility is for an application
>> to want more than 128 TiB address space on a machine with no more
>> than 64 TiB of RAM.  It is kind of a narrow use case, I think.
>
>Doesn't more address space increase the effectiveness of ASLR?  I
>thought KASLR, especially, was limited in its effectiveness because of
>a
>lack of address space.

The shortage of address space for KASLR is not addressable by LA57; rather, it would have to be addressed by compiling the kernel using a different (less efficient) memory model, presumably the "medium" memory model.
-- 
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