From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1162886AbcG0WHU (ORCPT ); Wed, 27 Jul 2016 18:07:20 -0400 Received: from cloudserver094114.home.net.pl ([79.96.170.134]:58027 "HELO cloudserver094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1162423AbcG0WHN (ORCPT ); Wed, 27 Jul 2016 18:07:13 -0400 From: "Rafael J. Wysocki" To: Josh Poimboeuf Cc: "Rafael J. Wysocki" , Ingo Molnar , Borislav Petkov , Pavel Machek , Linux PM list , Linux Kernel Mailing List , Thomas Gleixner , shuzzle@mailbox.org Subject: Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk Date: Thu, 28 Jul 2016 00:12:15 +0200 Message-ID: <2037077.DPom3MoXJk@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/4.5.0-rc1+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <20160727175918.5uvo4p54iuhuw7ss@treble> References: <16541580.dFLT14ScxF@vostro.rjw.lan> <20160727175918.5uvo4p54iuhuw7ss@treble> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wednesday, July 27, 2016 12:59:18 PM Josh Poimboeuf wrote: > On Wed, Jul 27, 2016 at 01:08:21AM +0200, Rafael J. Wysocki wrote: > > On Wed, Jul 27, 2016 at 12:42 AM, Rafael J. Wysocki wrote: > > > On Tuesday, July 26, 2016 04:53:19 PM Josh Poimboeuf wrote: > > >> On Tue, Jul 26, 2016 at 10:15:39PM +0200, Rafael J. Wysocki wrote: > > >> > On Tuesday, July 26, 2016 09:39:05 AM Josh Poimboeuf wrote: > > >> > > On Tue, Jul 26, 2016 at 01:32:28PM +0200, Rafael J. Wysocki wrote: > > >> > > > Hi, > > >> > > > > > >> > > > The following commit: > > >> > > > > > >> > > > commit 13523309495cdbd57a0d344c0d5d574987af007f > > >> > > > Author: Josh Poimboeuf > > >> > > > Date: Thu Jan 21 16:49:21 2016 -0600 > > >> > > > > > >> > > > x86/asm/acpi: Create a stack frame in do_suspend_lowlevel() > > >> > > > > > >> > > > do_suspend_lowlevel() is a callable non-leaf function which doesn't > > >> > > > honor CONFIG_FRAME_POINTER, which can result in bad stack traces. > > >> > > > > > >> > > > Create a stack frame for it when CONFIG_FRAME_POINTER is enabled. > > >> > > > > > >> > > > is reported to cause a resume-from-hibernation regression due to an attempt > > >> > > > to execute an NX page (we've seen quite a bit of that recently). > > >> > > > > > >> > > > I'm asking the reporter to try 4.7, but if the problem is still there, we'll > > >> > > > need to revert the above I'm afraid. > > >> > > > >> > So the bug is still there in 4.7 and it goes away after reverting the above > > >> > commit. I guess I'll send a revert then. > > >> > > >> Hm, the code in wakeup_64.S seems quite magical, but I can't figure out > > >> why this change causes a panic. Is it really causing the panic or is it > > >> uncovering some other bug? > > > > > > It doesn't matter really. > > > > > > It surely interacts with something in a really odd way, but that only means > > > that its impact goes far beyond what was expected when it was applied. Its > > > changelog is inadequate as a result and so on. > > > > > >> Maybe we should hold off on reverting until we understand the issue. > > > > > > Which very well may take forever. > > > > > > And AFAICS this is a fix for a theoretical issue and it *reliably* triggers a > > > very practical kernel panic for this particular reporter. I'd rather live > > > with the theoretical issue unfixed to be honest. > > > > Well, actually, the best part is that do_suspend_lowlevel() is not > > even called during hibernation or resume from it. It only is called > > during suspend-to-RAM. > > > > Question now is how the change made by the commit in question can > > affect hibernation which is an unrelated code path. We know for a > > fact that it does affect it, but how? > > Hm... I have a theory, but I'm not sure about it. I noticed that > x86_acpi_enter_sleep_state(), I think you mean x86_acpi_suspend_lowlevel(). > which is involved in suspend, overwrites > several global variables (e.g, initial_code) which are used by the CPU > boot code in head_64.S. But surprisingly, it doesn't restore those > variables to their original values after it resumes. Is the head_64.S code also used to bring up offline CPUs? If not, then this is not the problem, because hibernation doesn't use it for the boot CPU anyway. > So if a suspend and resume were done before the hibernate, those > variables would presumably have suspend-centric values, and the first > time a CPU is brought up during the hibernation restore operation, it > would jump to wakeup_long64() (the suspend resume function) instead of > start_secondary (which is the normal CPU boot function). > > So, if true, that would explain why my patch triggers a bug: > wakeup_long64() always[*] jumps to .Lresume_point, which my patch > affected. Because of the FRAME_END, it would pop an extra value off the > stack. So when restore_processor_state() returns, it would return to > whatever random address is on the stack after the real RIP. Which is > consistent with the oops from the bug. It had a bad instruction > pointer, which looked like a stack address. OK, so why doesn't it break resume from suspend to RAM? wakeup_long64 is invoked by the CPU startup code then and doesn't the FRAME_END affect that too? > But then again, maybe there's a hole in that theory, because how could > hibernate after suspend/resume possibly even work today if the CPU boot > goes to wakeup_long64() instead of start_secondary? Right. > So I could be missing something, or even completely off base. But the > missing restore of those variables does seem like a pretty huge > oversight. I wonder if the following patch would fix it? We'll need to ask the reporter. :-) > > diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c > index adb3eaf..cd76fc5 100644 > --- a/arch/x86/kernel/acpi/sleep.c > +++ b/arch/x86/kernel/acpi/sleep.c > @@ -45,6 +45,12 @@ acpi_status asmlinkage __visible x86_acpi_enter_sleep_state(u8 state) > */ > int x86_acpi_suspend_lowlevel(void) > { > +#ifdef CONFIG_64BIT > + unsigned long prev_initial_code; > +#ifdef CONFIG_SMP > + unsigned long prev_stack_start, prev_gdt_address, prev_initial_gs; > +#endif > +#endif > struct wakeup_header *header = > (struct wakeup_header *) __va(real_mode_header->wakeup_header); > > @@ -99,13 +105,18 @@ int x86_acpi_suspend_lowlevel(void) > saved_magic = 0x12345678; > #else /* CONFIG_64BIT */ > #ifdef CONFIG_SMP > + prev_stack_start = stack_start; > + prev_gdt_address = early_gdt_descr.address; > + prev_initial_gs = initial_gs; > + > stack_start = (unsigned long)temp_stack + sizeof(temp_stack); > early_gdt_descr.address = > (unsigned long)get_cpu_gdt_table(smp_processor_id()); > initial_gs = per_cpu_offset(smp_processor_id()); > #endif > + prev_initial_code = initial_code; > initial_code = (unsigned long)wakeup_long64; > - saved_magic = 0x123456789abcdef0L; > + saved_magic = 0x123456789abcdef0L; > #endif /* CONFIG_64BIT */ > > /* > @@ -115,6 +126,16 @@ int x86_acpi_suspend_lowlevel(void) > pause_graph_tracing(); > do_suspend_lowlevel(); > unpause_graph_tracing(); > + > +#ifdef CONFIG_64BIT > + initial_code = prev_initial_code; > +#ifdef CONFIG_SMP > + initial_gs = prev_initial_gs; > + early_gdt_descr.address = prev_gdt_address; > + stack_start = prev_stack_start; > +#endif > +#endif > + > return 0; > } >