linux-kernel - Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu

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Message-ID: <CAFULd4bpHkNzCzKed23mTTBWRyhPnOm91f+F6UE413VK+oFtMQ@mail.gmail.com>
Date:   Tue, 17 Oct 2023 21:11:46 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Nadav Amit <namit@...are.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()

On Tue, Oct 17, 2023 at 9:00 PM Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> On Tue, 17 Oct 2023 at 00:23, Nadav Amit <namit@...are.com> wrote:
> >
> > Yes, the FPU issue is the one that caused me to crash before.
>
> Uros, can you verify whether that patch of mine resolves the issue you saw?
>
> That patch is _technically_ an actual bug-fix, although right now our
> existing 'current' caching that depends on just CSE'ing the inline asm
> (and is apparently limited to only doing so within single basic
> blocks) doesn't actually trigger the bug in our __switch_to() logic in
> practice.

Unfortunately, it doesn't fix the oops :(

I'm testing your patch, together with the attached patch with the
current tip tree (that already has all necessary percpu stuff), and
get exactly the same oops in:

[    4.969657] cfg80211: Loading compiled-in X.509 certificates for
regulatory database
[    4.980712] modprobe (53) used greatest stack depth: 13480 bytes left
[    4.981048] BUG: kernel NULL pointer dereference, address: 0000000000000000
[    4.981830] #PF: supervisor write access in kernel mode
[    4.981830] #PF: error_code(0x0002) - not-present page
[    4.981830] PGD 0 P4D 0
[    4.981830] Oops: 0002 [#1] PREEMPT SMP PTI
[    4.981830] CPU: 1 PID: 54 Comm: kworker/u4:1 Not tainted
6.6.0-rc6-00406-g84ab57184ff4-dirty #2
[    4.981830] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS 1.16.2-1.fc37 04/01/2014
[    4.981830] RIP: 0010:begin_new_exec+0x8f2/0xa30
[    4.981830] Code: 31 f6 e8 c1 49 f9 ff e9 3c fa ff ff 31 f6 4c 89
ef e8 b2 4a f9 ff e9 19 fa ff ff 31 f6 4c 89 ef e8 23 4a f9 ff e9 ea
fa ff ff <f0>
41 ff 0c 24 0f 85 55 fb ff ff 4c 89 e7 e8 4b 02 df ff e9 48 fb
[    4.981830] RSP: 0000:ffffa505401f3d68 EFLAGS: 00010246
[    4.981830] RAX: 0000000000000000 RBX: ffff89ed809e9f00 RCX: 0000000000000000
[    4.981830] RDX: 0000000000000000 RSI: ffff89ed80e6c000 RDI: ffff89ed809ea718
[    4.981830] RBP: ffff89ed8039ee00 R08: 00000000fffffffe R09: 00000000ffffffff
[    4.981830] R10: 000001ffffffffff R11: 0000000000000001 R12: 0000000000000000
[    4.981830] R13: 0000000000000000 R14: ffff89ed809ea718 R15: ffff89ed80e6c000
[    4.981830] FS:  0000000000000000(0000) GS:ffff89ee24900000(0000)
knlGS:0000000000000000
[    4.981830] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    4.981830] CR2: 0000000000000000 CR3: 00000001003a0000 CR4: 00000000000406f0
[    4.981830] Call Trace:
[    4.981830]  <TASK>
[    4.981830]  ? __die+0x1e/0x60
[    4.981830]  ? page_fault_oops+0x17b/0x470
[    4.981830]  ? search_module_extables+0x14/0x50
[    4.981830]  ? exc_page_fault+0x66/0x140
[    4.981830]  ? asm_exc_page_fault+0x26/0x30
[    4.981830]  ? begin_new_exec+0x8f2/0xa30
[    4.981830]  ? begin_new_exec+0x3ce/0xa30
[    4.981830]  ? load_elf_phdrs+0x67/0xb0
[    4.981830]  load_elf_binary+0x2bb/0x1770
[    4.981830]  ? __kernel_read+0x136/0x2d0
[    4.981830]  bprm_execve+0x277/0x630
[    4.981830]  kernel_execve+0x145/0x1a0
[    4.981830]  call_usermodehelper_exec_async+0xcb/0x180
[    4.981830]  ? __pfx_call_usermodehelper_exec_async+0x10/0x10
[    4.981830]  ret_from_fork+0x2f/0x50
[    4.981830]  ? __pfx_call_usermodehelper_exec_async+0x10/0x10
[    4.981830]  ret_from_fork_asm+0x1b/0x30
[    4.981830]  </TASK>
[    4.981830] Modules linked in:
[    4.981830] CR2: 0000000000000000
[    5.052612] ---[ end trace 0000000000000000 ]---
[    5.053833] RIP: 0010:begin_new_exec+0x8f2/0xa30
[    5.055065] Code: 31 f6 e8 c1 49 f9 ff e9 3c fa ff ff 31 f6 4c 89
ef e8 b2 4a f9 ff e9 19 fa ff ff 31 f6 4c 89 ef e8 23 4a f9 ff e9 ea
fa ff ff <f0>
41 ff 0c 24 0f 85 55 fb ff ff 4c 89 e7 e8 4b 02 df ff e9 48 fb
[    5.059476] RSP: 0000:ffffa505401f3d68 EFLAGS: 00010246
[    5.060780] RAX: 0000000000000000 RBX: ffff89ed809e9f00 RCX: 0000000000000000
[    5.062483] RDX: 0000000000000000 RSI: ffff89ed80e6c000 RDI: ffff89ed809ea718
[    5.064190] RBP: ffff89ed8039ee00 R08: 00000000fffffffe R09: 00000000ffffffff
[    5.065908] R10: 000001ffffffffff R11: 0000000000000001 R12: 0000000000000000
[    5.067625] R13: 0000000000000000 R14: ffff89ed809ea718 R15: ffff89ed80e6c000
[    5.069343] FS:  0000000000000000(0000) GS:ffff89ee24900000(0000)
knlGS:0000000000000000
[    5.071313] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    5.072732] CR2: 0000000000000000 CR3: 00000001003a0000 CR4: 00000000000406f0
[    5.074439] Kernel panic - not syncing: Fatal exception
[    5.075028] Kernel Offset: 0xcc00000 from 0xffffffff81000000
(relocation range: 0xffffffff80000000-0xffffffffbfffffff)



Uros.

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