Re: qemu-x86_64 booting with 8.0.0 stil see int3: when running LTP tracing testing.
From: Richard W.M. Jones
Date: Wed Jul 05 2023 - 12:41:15 EST
On Wed, Jul 05, 2023 at 06:36:43PM +0200, Richard Henderson wrote:
> No, I thought it would be the fix for 8.0.0.
Thanks for the suggestion anyway.
Am I right in thinking that tb_invalidate_phys_page() ought to be
called when the kernel self-modifies its text segment? If there's
some function that we expect to be called in this case then I can
instrument it.
Rich.
> r~
>
> On Wed, 5 July 2023, 18:35 Richard W.M. Jones, <rjones@xxxxxxxxxx> wrote:
>
> On Wed, Jul 05, 2023 at 06:32:30PM +0200, Richard Henderson wrote:
> > https://gitlab.com/qemu-project/qemu/-/commit/
> > 3307e08c6f142bb3d2406cfbc0ee19359748b51a
>
> I've got that patch in my qemu tree. Do you suspect it's
> wrong and want me to try reverting it?
>
> Rich.
>
> > r~
> >
> > On Wed, 5 July 2023, 18:28 Richard W.M. Jones, <rjones@xxxxxxxxxx> 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] <TASK>
> > > [ 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] </TASK>
> > > [ 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
> > > <something in the clock or timer code> -> 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
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> >
> >
>
> --
> Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/
> ~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
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>
--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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