From owner-freebsd-current@FreeBSD.ORG Fri Jun 19 16:39:58 2009 Return-Path: Delivered-To: freebsd-current@FreeBSD.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E9254106566C; Fri, 19 Jun 2009 16:39:58 +0000 (UTC) (envelope-from avg@icyb.net.ua) Received: from citadel.icyb.net.ua (citadel.icyb.net.ua [212.40.38.140]) by mx1.freebsd.org (Postfix) with ESMTP id EE5878FC0A; Fri, 19 Jun 2009 16:39:57 +0000 (UTC) (envelope-from avg@icyb.net.ua) Received: from odyssey.starpoint.kiev.ua (alpha-e.starpoint.kiev.ua [212.40.38.101]) by citadel.icyb.net.ua (8.8.8p3/ICyb-2.3exp) with ESMTP id TAA07936; Fri, 19 Jun 2009 19:39:54 +0300 (EEST) (envelope-from avg@icyb.net.ua) Message-ID: <4A3BBF5A.6060702@icyb.net.ua> Date: Fri, 19 Jun 2009 19:39:54 +0300 From: Andriy Gapon User-Agent: Thunderbird 2.0.0.21 (X11/20090406) MIME-Version: 1.0 To: Thomas Backman References: <949B5884-5303-4EFF-AC7D-293640FFA012@exscape.org> <0C235698-3ED2-4AE9-A7D1-5DC56D8324A4@exscape.org> <200905212129.47892.mel.flynn+fbsd.current@mailing.thruhere.net> <44F486FA-E798-448D-BE31-F7A51EF1F612@exscape.org> <60173AF0-7E54-4BDD-8927-0DADA9DAD1B4@exscape.org> <20090522200306.GE2630@atarininja.org> <20090617225849.GB28509@atarininja.org> <4A3A1D27.4010802@icyb.net.ua> In-Reply-To: X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Alan Cox , freebsd-current@FreeBSD.org, John Birrell , John Baldwin Subject: Re: DTrace panic while probing syscall::open (and possibly many others) X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 19 Jun 2009 16:39:59 -0000 on 18/06/2009 14:42 Thomas Backman said the following: > > On Jun 18, 2009, at 12:55 PM, Andriy Gapon wrote: > >> on 18/06/2009 12:43 Thomas Backman said the following: >>> >>> at dtrace_isa.c:527 >>> #14 0xffffffff816b31fc in dtrace_copyinstr (uaddr=34365163021, >>> kaddr=18446743524025463312, size=256, flags=0xffffffff8146e0c0) >>> at dtrace_isa.c:558 >> >> kaddr=18446743524025463312 == FFFFFF8004467210 >> I think kernelbase on amd64 is 0xFFFFFFFF80000000. >> FFFFFF8004467210 kaddr >> is smaller than >> FFFFFFFF80000000 kernelbase >> >> The numbers do look suspiciously similar, so I am not sure if you are >> seeing a >> race or a real bug somewhere. >> -- >> Andriy Gapon > Hmmm... > Looking around a bit for these numbers, I found, in > /sys/amd64/include/vmparam.h: > > /* > * Virtual addresses of things. Derived from the page directory and > * page table indexes from pmap.h for precision. > * > * 0x0000000000000000 - 0x00007fffffffffff user map > * 0x0000800000000000 - 0xffff7fffffffffff does not exist (hole) > * 0xffff800000000000 - 0xffff804020100fff recursive page table (512GB > slot) > * 0xffff804020101000 - 0xfffffeffffffffff unused > * 0xffffff0000000000 - 0xffffff7fffffffff 512GB direct map mappings > * 0xffffff8000000000 - 0xffffffffffffffff 512GB kernel map > * > * Within the kernel map: > * > * 0xffffffff80000000 KERNBASE > */ > > So, kaddr is inside the "kernel map", but not KERNBASE. What this means, > I have no clue whatsoever. (I'm not a kernel developer and I don't know > too much about (virtual) memory either!) Thomas, I think that you were correct that one needs to be somewhat of a VM expert here. It seems that amd64 is the only[?] platform where KERNBASE != VM_MIN_KERNEL_ADDRESS (0xffffffff80000000 and 0xffffff8000000000 correspondingly). That makes the assert in sys/cddl/dev/dtrace/amd64/dtrace_isa.c bogus in my opinion: static int dtrace_copycheck(uintptr_t uaddr, uintptr_t kaddr, size_t size) { ASSERT(kaddr >= kernelbase && kaddr + size >= kaddr); If the purpose of the assert is to ensure that [kaddr:kaddr+size) is within kernel memory, then it should use VM_MIN_KERNEL_ADDRESS instead of KERNBASE. Or maybe even use something like the macro in sys/amd64/include/stack.h: #define INKERNEL(va) (((va) >= DMAP_MIN_ADDRESS && (va) < DMAP_MAX_ADDRESS) \ || ((va) >= VM_MIN_KERNEL_ADDRESS && (va) < VM_MAX_KERNEL_ADDRESS)) The above is just my understanding, not a fact, so I am CC-ing people that are really knowledgeable of our VM and the porter/author of our DTrace code too. -- Andriy Gapon