linux-kernel - Re: [PATCH] x86/percpu: Return correct variable from current_top_of

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Date:   Tue, 24 Oct 2023 17:56:29 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Uros Bizjak <ubizjak@...il.com>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/percpu: Return correct variable from
 current_top_of_stack()

On Tue, Oct 24, 2023 at 04:28:14PM +0200, Uros Bizjak wrote:
> current_top_of_stack() should return variable from _seg_gs
> qualified named address space when CONFIG_USE_X86_SEG_SUPPORT
> is enbled.

I presume you're sending those two in order to fix stuff like the splat
below which fires in my guest with latest Linus + latest tip/master
lineup.

Because disabling CONFIG_USE_X86_SEG_SUPPORT fixes it.

I'm wondering that close to the merge window whether we should delay
all that new and fancy percpu stuff one more round until it is tested
more widely...

[    1.623994] kprobes: kprobe jump-optimization is enabled. All kprobes are optimized if possible.
[    1.627398] HugeTLB: registered 1.00 GiB page size, pre-allocated 0 pages
[    1.627101] BUG: unable to handle page fault for address: 000000000002f0d8
[    1.629645] HugeTLB: 16380 KiB vmemmap can be freed for a 1.00 GiB page
[    1.628158] #PF: supervisor read access in kernel mode
[    1.628161] #PF: error_code(0x0000) - not-present page
[    1.628163] PGD 0 P4D 0 
[    1.628167] Oops: 0000 [#1] PREEMPT SMP
[    1.628171] CPU: 1 PID: 10 Comm: kworker/u32:0 Not tainted 6.6.0-rc7+ #1
[    1.631566] HugeTLB: registered 2.00 MiB page size, pre-allocated 0 pages
[    1.629156] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
[    1.632494] HugeTLB: 28 KiB vmemmap can be freed for a 2.00 MiB page
[    1.629990] Workqueue: ftrace_check_wq ftrace_check_work_func
[    1.631041] RIP: 0010:raw_irqentry_exit_cond_resched+0x16/0x50
[    1.631041] Code: 00 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 65 f7 05 d4 ff ef 7e ff ff ff 7f 75 21 <48> 8b 05 db ff ef 7e 48 29 e0 48 3d ff 3f 00 00 77 19 65 48 8b 05
[    1.631041] RSP: 0018:ffffc9000005bab8 EFLAGS: 00010046
[    1.631041] RAX: 0000000000000000 RBX: 0000000000000000 RCX: 000000000002f900
[    1.631041] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffc9000005bac8
[    1.631041] RBP: 0000000000000000 R08: 0000000000000002 R09: 0000000000000001
[    1.631041] R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
[    1.631041] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
[    1.631041] FS:  0000000000000000(0000) GS:ffff88807da40000(0000) knlGS:0000000000000000
[    1.631041] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    1.631041] CR2: 000000000002f0d8 CR3: 0000000002416000 CR4: 00000000003506f0
[    1.631041] Call Trace:
[    1.631041]  <TASK>
[    1.631041]  ? __die+0x31/0x80
[    1.631041]  ? page_fault_oops+0x160/0x440
[    1.631041]  ? exc_page_fault+0x74/0x150
[    1.631041]  ? asm_exc_page_fault+0x26/0x30
[    1.631041]  ? raw_irqentry_exit_cond_resched+0x16/0x50
[    1.631041]  irqentry_exit+0x21/0x60
[    1.631041]  asm_sysvec_apic_timer_interrupt+0x1a/0x20
[    1.631041] RIP: 0010:get_symbol_offset+0x26/0x60
[    1.631041] Code: 90 90 90 90 0f 1f 44 00 00 48 89 f8 48 c1 e8 08 8b 04 85 80 4f 0b 82 48 05 88 af f1 81 81 e7 ff 00 00 00 74 25 31 c9 0f b6 10 <84> d2 79 0e 0f b6 70 01 83 e2 7f c1 e6 07 09 f2 ff c2 ff c2 ff c1

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette