From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f198.google.com (mail-pf0-f198.google.com [209.85.192.198]) by kanga.kvack.org (Postfix) with ESMTP id 478706B0279 for ; Fri, 26 May 2017 15:21:55 -0400 (EDT) Received: by mail-pf0-f198.google.com with SMTP id 62so24258352pft.3 for ; Fri, 26 May 2017 12:21:55 -0700 (PDT) Received: from mail.zytor.com (terminus.zytor.com. [65.50.211.136]) by mx.google.com with ESMTPS id 21si1755264pgh.402.2017.05.26.12.21.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 May 2017 12:21:54 -0700 (PDT) Date: Fri, 26 May 2017 11:24:39 -0700 In-Reply-To: References: <20170525203334.867-1-kirill.shutemov@linux.intel.com> <20170526130057.t7zsynihkdtsepkf@node.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCHv1, RFC 0/8] Boot-time switching between 4- and 5-level paging From: hpa@zytor.com Message-ID: <83F4880B-5D1F-4576-A9B6-7DDF4173E2E5@zytor.com> Sender: owner-linux-mm@kvack.org List-ID: To: Linus Torvalds , "Kirill A. Shutemov" Cc: "Kirill A. Shutemov" , Andrew Morton , the arch/x86 maintainers , Thomas Gleixner , Ingo Molnar , Andi Kleen , Dave Hansen , Andy Lutomirski , "linux-arch@vger.kernel.org" , linux-mm , Linux Kernel Mailing List On May 26, 2017 8:51:48 AM PDT, Linus Torvalds wrote: >On Fri, May 26, 2017 at 6:00 AM, Kirill A=2E Shutemov > wrote: >> >> I don't see how kernel threads can use 4-level paging=2E It doesn't >work >> from virtual memory layout POV=2E Kernel claims half of full virtual >address >> space for itself -- 256 PGD entries, not one as we would effectively >have >> in case of switching to 4-level paging=2E For instance, addresses, >where >> vmalloc and vmemmap are mapped, are not canonical with 4-level >paging=2E > >I would have just assumed we'd map the kernel in the shared part that >fits in the top 47 bits=2E > >But it sounds like you can't switch back and forth anyway, so I guess >it's moot=2E > >Where *is* the LA57 documentation, btw? I had an old x86 architecture >manual, so I updated it, but LA57 isn't mentioned in the new one >either=2E > > Linus As one of the major motivations for LA57 is that we expect that we will ha= ve machines with more than 2^46 bytes of memory in the near future, it isn'= t feasible in most cases to do per-VM LA57=2E The only case where that even has any utility is for an application to wan= t more than 128 TiB address space on a machine with no more than 64 TiB of = RAM=2E It is kind of a narrow use case, I think=2E --=20 Sent from my Android device with K-9 Mail=2E Please excuse my brevity=2E -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org