linux-kernel - Re: [PATCH 00/16] Entry stuff, in decent shape now

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Date:   Tue, 21 Nov 2017 07:59:25 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 00/16] Entry stuff, in decent shape now

On Mon, Nov 20, 2017 at 11:33 PM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...nel.org> wrote:
>
>> This sets up stack switching, including for SYSCALL.  I think it's
>> in decent shape.
>>
>> Known issues:
>>  - KASAN is likely to be busted.  This could be fixed either by teaching
>>    KASAN that cpu_entry_area contains valid stacks (I have no clue how
>>    to go about doing this) or by rigging up the IST entry code to switch
>>    RSP to point to the direct-mapped copy of the stacks before calling
>>    into non-KASAN-excluded C code.
>>
>>  - 32-bit kernels are failing the sigreturn_32 test.  But they're also
>>    failing without the patches, so I'm not sure this is a bug in the
>>    series per se.  Needs further investigation.  (Off the top of my head,
>>    this could be further fallout from Thomas's IDT rework.)
>>
>>  - I think we're going to want a way to turn the stack switching on and
>>    off either at boot time or at runtime.  It should be fairly straightforward
>>    to make it work.
>>
>>  - I think the ORC unwinder isn't so good at dealing with stack overflows.
>>    It bails too early (I think), resulting in lots of ? entries.  This
>>    isn't a regression with this series -- it's just something that could
>>    be improved.
>
> Another problem I just found: IRQ tracing appears busted on 64-bit kernels - with
> lockdep enabled I get this boot warning:
>
>  [    4.309026] WARNING: CPU: 10 PID: 222 at kernel/locking/lockdep.c:3924 check_flags.part.45+0x1a5/0x1b0
>  ...
>  [    4.309026] possible reason: unannotated irqs-off.
>
> That's on a x86-64 defconfig-ish kernel with CONFIG_PROVE_LOCKING=y, running on an
> AMD system. Full splat below.
>
> Thanks,
>
>         Ingo
>
> [    4.272197] LVT offset 0 assigned for vector 0x400
> [    4.278486] perf: AMD IBS detected (0x000000ff)
> [    4.284786] kvm: Nested Virtualization enabled
> [    4.289447] kvm: Nested Paging enabled
> [    4.308496] DEBUG_LOCKS_WARN_ON(current->hardirqs_enabled)
> [    4.308512] ------------[ cut here ]------------
> [    4.309026] WARNING: CPU: 10 PID: 222 at kernel/locking/lockdep.c:3924 check_flags.part.45+0x1a5/0x1b0
> [    4.309026] Modules linked in:
> [    4.309026] CPU: 10 PID: 222 Comm: modprobe Not tainted 4.14.0-01345-g9490674-dirty #1
> [    4.309026] Hardware name: Supermicro H8DG6/H8DGi/H8DG6/H8DGi, BIOS 2.0b       03/01/2012
> [    4.309026] task: ffff880814b08000 task.stack: ffffc90007dcc000
> [    4.309026] RIP: 0010:check_flags.part.45+0x1a5/0x1b0
> [    4.309026] RSP: 0018:ffffc90007dcfeb0 EFLAGS: 00010082
> [    4.309026] RAX: 000000000000002e RBX: ffff880814b08000 RCX: 0000000000000000
> [    4.309026] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff81152e76
> [    4.309026] RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000000
> [    4.309026] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> [    4.309026] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000000
> [    4.309026] FS:  0000000000000000(0000) GS:ffff880817c80000(0000) knlGS:0000000000000000
> [    4.309026] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [    4.309026] CR2: 00007f8badc39218 CR3: 000000081584b000 CR4: 00000000000406e0
> [    4.309026] Call Trace:
> [    4.309026]  lock_acquire+0x11a/0x1d0
> [    4.309026]  vtime_user_exit+0x3c/0xa0
> [    4.309026]  ? __context_tracking_exit.part.4+0x45/0x130
> [    4.309026]  __context_tracking_exit.part.4+0x45/0x130
> [    4.309026]  do_syscall_64+0x13f/0x220
> [    4.309026]  entry_SYSCALL64_slow_path+0x25/0x25

I'm not reproducing this.  On quick inspection, the only potential
issue I see is that native_gs_load_index is missing IRQ tracing
annotations, but I don't see why this series would have any particular
effect on that.

Do you see it on my latest tree?

--Andy