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

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Date:   Tue, 21 Nov 2017 08:33:01 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     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


* 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
[    4.309026] RIP: 0033:0x7f8bada2e42a
[    4.309026] RSP: 002b:00007fffba194e38 EFLAGS: 00000246 ORIG_RAX: 000000000000000c
[    4.309026] RAX: ffffffffffffffda RBX: 0000000000400040 RCX: 00007f8bada2e42a
[    4.309026] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[    4.309026] RBP: 0000000000000009 R08: 000000000000037f R09: 0000000000000064
[    4.309026] R10: 00000000178bfbff R11: 0000000000000246 R12: 00007f8bada19ce0
[    4.309026] R13: 0000000000000000 R14: 0000000000403308 R15: 0000000000001000
[    4.309026] Code: c6 9c f6 ed 81 48 c7 c7 e2 88 ed 81 e8 a0 32 01 00 0f ff e9 ef fe ff ff 48 c7 c6 9d f6 ed 81 48 c7 c7 e2 88 ed 81 e8 86 32 01 00 <0f> ff e9 5f ff ff ff 0f 1f 40 00 41 57 41 56 41 55 41 54 55 53 
[    4.309026] ---[ end trace bdfbcef9b01b1cbb ]---
[    4.309026] possible reason: unannotated irqs-off.
[    4.309026] irq event stamp: 445
[    4.309026] hardirqs last  enabled at (445): [<ffffffff81a4ae23>] swapgs_restore_regs_and_return_to_usermode+0x0/0x3c
[    4.309026] hardirqs last disabled at (444): [<ffffffff81a4bac6>] error_exit+0x6/0x20
[    4.309026] softirqs last  enabled at (24): [<ffffffff81a4e6f7>] __do_softirq+0x3b7/0x468
[    4.309026] softirqs last disabled at (7): [<ffffffff810ebec4>] irq_exit+0xc4/0xd0
[    4.572172] audit: initializing netlink subsys (disabled)
[    4.577846] audit: type=2000 audit(1511245386.576:1): state=initialized audit_enabled=0 res=1
[    4.578742] workingset: timestamp_bits=53 max_order=24 bucket_order=0
[    4.582656] SELinux:  Registering netfilter hooks
[    4.606349] NET: Registered protocol family 38