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

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Message-ID: <CAFULd4anCehMUeAjanZyxLz+w5spvnrdUhjg0wRTv5sopHt0ag@mail.gmail.com>
Date:   Tue, 24 Oct 2023 18:05:06 +0200
From:   Uros Bizjak <ubizjak@...il.com>
To:     Borislav Petkov <bp@...en8.de>
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 5:56 PM Borislav Petkov <bp@...en8.de> wrote:
>
> 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.

Yes, the first one is the fix, the second one is only tangentially
related to the fix.

> 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...

The percpu stuff won't be merged for 6.7, it will have to sit out until 6.8.

Thanks,
Uros.


>
> [    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