From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Ropert Subject: [RESEND] Question about recursive mappings Date: Mon, 22 May 2006 11:15:58 +0200 Message-ID: <4471814E.2070302@adviseo.fr> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org [Previous one didn't hit list after 3 days, trying a resend, sorry if both finally show up] Hi, are recursive mappings (ie: a page table entry pointing back to itself) supported by Xen (on x86_64 at least)? I'm asking cause i'm seeing many error logs from get_page_type() telling something like "saw L3_page_table expected L2_page_table" or "saw L4_page_table expected L3_page_table" (finally leading to a failing mmu_update, i guess others happens on user pagetables switches). Or maybe is there any workaround needed? (I think i saw something like setting entry to 0 first then to the recursive entry somewhere, but can't remember where). By the way, i'm using recursive mappings in kernel page directory (which seems ok) and i temporay make user page directory recursive when i map a user PGD in kernel space (mapping user PGD to a L4 entry of kernel tables, then using kernel L4 slot and user PGD recursive entry to access user page tables). [edit] Done some little research about the problem. Seems like NetBSD use the same thing and works, but there is no x86_64 ports for now. I'm starting to think that may be a x86_64 issue, maybe because recursive mappings don't lead to conflicting types with only 2 levels. Xen interface states that a page can only be of one type (PGD, PT, LDT, GDT and R/W). I don't know why there is a need to distinguish page table levels, but i'm afraid this restriction will conflit with some MMU implementation on x86_64 like NetBSD and OpenBSD, and maybe others (FreeBSD on top of my mind, don't know how much the pmap implementation diverged). [/edit] Regards, Mathieu