From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B3CE8EB64DA for ; Wed, 5 Jul 2023 16:39:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231466AbjGEQiy (ORCPT ); Wed, 5 Jul 2023 12:38:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53812 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229910AbjGEQiv (ORCPT ); Wed, 5 Jul 2023 12:38:51 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C6EDA10EA for ; Wed, 5 Jul 2023 09:38:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1688575081; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=f+BIFPuADYbd26Hky4KRHtBDGMxjN7kUaiaPVMFcqU0=; b=SweReg4GXOzVSC6hfRfz8zo/EYy8V8X3SAJmYUaWy19CGmLslN6QaJQzvsnfvtEntDR6OY Zh3lUMP9fwEn/ykxAbxObTTJqJUvprp+twktMf/ZXNVE+1gPCBIrazENjVAm+fAenA9lLd 9koOIHU7EMOYNkkpIGpaQX5l1N9JCDo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-358-pd3MsW3jNJ2ZrOPRGlY5dg-1; Wed, 05 Jul 2023 12:37:58 -0400 X-MC-Unique: pd3MsW3jNJ2ZrOPRGlY5dg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id E9830802666; Wed, 5 Jul 2023 16:37:57 +0000 (UTC) Received: from localhost (unknown [10.42.28.237]) by smtp.corp.redhat.com (Postfix) with ESMTP id B42ED18EB4; Wed, 5 Jul 2023 16:37:57 +0000 (UTC) Date: Wed, 5 Jul 2023 17:37:57 +0100 From: "Richard W.M. Jones" To: Richard Henderson Cc: Peter Zijlstra , Arnd Bergmann , Naresh Kamboju , Anders Roxell , Daniel =?iso-8859-1?Q?D=EDaz?= , Benjamin Copeland , lkml - Kernel Mailing List , the arch/x86 maintainers , Paolo Bonzini Subject: Re: qemu-x86_64 booting with 8.0.0 stil see int3: when running LTP tracing testing. Message-ID: <20230705163757.GK7636@redhat.com> References: <2d7595b1-b655-4425-85d3-423801bce644@app.fastmail.com> <20230621160655.GL2053369@hirez.programming.kicks-ass.net> <20230704074620.GA17440@redhat.com> <20230705162830.GC17440@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 3.1 on 10.11.54.5 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 05, 2023 at 06:32:30PM +0200, Richard Henderson wrote: > https://gitlab.com/qemu-project/qemu/-/commit/ > 3307e08c6f142bb3d2406cfbc0ee19359748b51a FWIW reverting this commit (alone) causes qemu to throw this assertion: qemu-system-x86_64: ../accel/tcg/tb-maint.c:1096: tb_invalidate_phys_page_range__locked: Assertion `((start ^ last) & ((target_long)-1 << 12)) == 0' failed. I've seen this bug happen on both very old and very new versions of qemu (even back to 6.0), so I don't think the bug is caused by or fixed by any recent change. Rich. > r~ > > On Wed, 5 July 2023, 18:28 Richard W.M. Jones, wrote: > > On Tue, Jul 04, 2023 at 08:46:20AM +0100, Richard W.M. Jones wrote: > > We have been having the same sort of problem > > (https://bugzilla.redhat.com/show_bug.cgi?id=2216496).  It's another > > of those bugs that requires hundreds or thousands of boot iterations > > before you can see it.  There is a test in comment 27 but it requires > > guestfish and some hacking to work.  I'll try to come up with a > > cleaner test later. > > > > We see stack traces like: > > > > [    3.081939] clocksource: acpi_pm: mask: 0xffffff max_cycles: 0xffffff, > max_idle_ns: 2085701024 ns > > [    3.082266] clocksource: Switched to clocksource acpi_pm > > [    3.090201] NET: Registered PF_INET protocol family > > [    3.093098] int3: 0000 [#1] PREEMPT SMP NOPTI > > [    3.093098] CPU: 3 PID: 1 Comm: swapper/0 Not tainted > 6.4.0-10173-ga901a3568fd2 #8 > > [    3.093098] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS > rel-1.16.2-0-gea1b7a073390-prebuilt.qemu.org 04/01/2014 > > [    3.093098] RIP: 0010:__mod_timer+0x1c3/0x370 > > [    3.093098] Code: 00 00 41 bd ff ff ff ff 31 d2 4c 89 f6 4c 89 ff e8 > f2 ef ff ff 41 89 c4 85 c0 75 09 83 e3 01 0f 85 54 ff ff ff 41 8b 4f 20 66 > <90> f7 c1 00 00 10 00 0f 84 23 01 00 00 48 c7 c3 40 cc 01 00 65 48 > > [    3.093098] RSP: 0018:ffffaf1600013e00 EFLAGS: 00000046 > > [    3.093098] RAX: 0000000000000000 RBX: 0000000000000000 RCX: > 0000000000280003 > > [    3.093098] RDX: 0000000000000000 RSI: ffff9aa90fd9dec0 RDI: > ffffffff8441e4b8 > > [    3.093098] RBP: 00000000fffc200d R08: ffffffff8441e4a0 R09: > ffffffff8441e4b8 > > [    3.093098] R10: 0000000000000001 R11: 000000000002e990 R12: > 0000000000000000 > > [    3.093098] R13: 00000000ffffffff R14: ffff9aa90fd9dec0 R15: > ffffffff8441e4b8 > > [    3.093098] FS:  0000000000000000(0000) GS:ffff9aa90fd80000(0000) > knlGS:0000000000000000 > > [    3.093098] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [    3.093098] CR2: 0000000000000000 CR3: 000000004e02e000 CR4: > 0000000000750ee0 > > [    3.093098] PKRU: 55555554 > > [    3.093098] Call Trace: > > [    3.093098]  > > [    3.093098]  ? die+0x31/0x80 > > [    3.093098]  ? exc_int3+0x10e/0x120 > > [    3.093098]  ? asm_exc_int3+0x39/0x40 > > [    3.093098]  ? __mod_timer+0x1c3/0x370 > > [    3.093098]  ? __mod_timer+0x1c3/0x370 > > [    3.093098]  queue_delayed_work_on+0x23/0x30 > > [    3.093098]  neigh_table_init+0x1bb/0x2e0 > > [    3.093098]  arp_init+0x12/0x50 > > [    3.093098]  inet_init+0x15b/0x2f0 > > [    3.093098]  ? __pfx_inet_init+0x10/0x10 > > [    3.093098]  do_one_initcall+0x58/0x230 > > [    3.093098]  kernel_init_freeable+0x199/0x2d0 > > [    3.093098]  ? __pfx_kernel_init+0x10/0x10 > > [    3.093098]  kernel_init+0x15/0x1b0 > > [    3.093098]  ret_from_fork+0x2c/0x50 > > [    3.093098]  > > [    3.093098] Modules linked in: > > [    3.093098] ---[ end trace 0000000000000000 ]--- > > [    3.093098] RIP: 0010:__mod_timer+0x1c3/0x370 > > [    3.093098] Code: 00 00 41 bd ff ff ff ff 31 d2 4c 89 f6 4c 89 ff e8 > f2 ef ff ff 41 89 c4 85 c0 75 09 83 e3 01 0f 85 54 ff ff ff 41 8b 4f 20 66 > <90> f7 c1 00 00 10 00 0f 84 23 01 00 00 48 c7 c3 40 cc 01 00 65 48 > > [    3.093098] RSP: 0018:ffffaf1600013e00 EFLAGS: 00000046 > > [    3.093098] RAX: 0000000000000000 RBX: 0000000000000000 RCX: > 0000000000280003 > > [    3.093098] RDX: 0000000000000000 RSI: ffff9aa90fd9dec0 RDI: > ffffffff8441e4b8 > > [    3.093098] RBP: 00000000fffc200d R08: ffffffff8441e4a0 R09: > ffffffff8441e4b8 > > [    3.093098] R10: 0000000000000001 R11: 000000000002e990 R12: > 0000000000000000 > > [    3.093098] R13: 00000000ffffffff R14: ffff9aa90fd9dec0 R15: > ffffffff8441e4b8 > > [    3.093098] FS:  0000000000000000(0000) GS:ffff9aa90fd80000(0000) > knlGS:0000000000000000 > > [    3.093098] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > > [    3.093098] CR2: 0000000000000000 CR3: 000000004e02e000 CR4: > 0000000000750ee0 > > [    3.093098] PKRU: 55555554 > > [    3.093098] Kernel panic - not syncing: Fatal exception in interrupt > > > > There are many variations, but the common pattern seems to be > > -> int3 exception > > > > It only happens under qemu TCG (software emulation). > > > > It goes away if we recompile qemu without MTTCG support. > > > > It only happens with -smp enabled, we are using qemu -smp 4 > > > > We are using qemu-system-x86_64 full system emulation on x86_64 host > > (ie. forcing KVM off). > > > > It happens with the latest upstream kernel and qemu, compiled from > > source. > > I got a bit further on this one. > > The bug happens in the code that updates the static branch used for at > least these two keys: > >   static DEFINE_STATIC_KEY_FALSE(__sched_clock_stable); >   DEFINE_STATIC_KEY_FALSE(timers_migration_enabled); > > There are probably others (it seems a generic problem with how static > branches are handled by TCG), but I only see the bug for those two. > > When the static branch is updated we end up calling > arch/x86/kernel/alternative.c:text_poke_bp_batch().  It's best to read > the description of that function to see where int3 is used: > >   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/ > arch/x86/kernel/alternative.c#n2086 > > I modified the qemu TCG int3 helper so it dumps the code at %rip when > the interrupt fires, and I can actually see the changes in the above > function happen, first int3 being written, then the end of the nop, > then the int3 being overwritten with the first byte of the nop. > > Unfortunately the int3 still fires after the code has been completely > rewritten to its final (ie nop) value. > > This seems to indicate to me that neither the self-write to the kernel > text segment, nor sync_core (implemented by a "iret to self" trick) > invalidates the qemu TCG translation block containing the old int3 > helper call.  Thus we (qemu) never "see" the new nop, we keep > emulating int3, and that causes the kernel to crash. > > I added print statements inside tb_invalidate_phys_page() and this > function seems never to be called at all.  It's my understanding that > at least the kernel writing to its text segment ought to cause > tb_invalidate_phys_page() to be called, but I'm not super-familiar > with this qemu code. > > Richard Henderson - do you have any suggestions? > > Rich. > > -- > Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/ > ~rjones > Read my programming and virtualization blog: http://rwmj.wordpress.com > libguestfs lets you edit virtual machines.  Supports shell scripting, > bindings from many languages.  http://libguestfs.org > > -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-top is 'top' for virtual machines. Tiny program with many powerful monitoring features, net stats, disk stats, logging, etc. http://people.redhat.com/~rjones/virt-top