linux-kernel - Re: [PATCH v2] x86: add hintable NOPs emulation

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Message-ID: <0ffa7c6e-f32f-4966-85df-3ee5f2426e9e@orca.pet>
Date: Sun, 31 Aug 2025 16:34:05 +0200
From: Marcos Del Sol Vives <marcos@...a.pet>
To: kernel test robot <oliver.sang@...el.com>
Cc: oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
 Peter Zijlstra <peterz@...radead.org>, Kees Cook <kees@...nel.org>,
 "Xin Li (Intel)" <xin@...or.com>, Sabyrzhan Tasbolatov <snovitoll@...il.com>
Subject: Re: [PATCH v2] x86: add hintable NOPs emulation

El 30/08/2025 a las 8:56, kernel test robot escribió:
> [   24.176151][ T2696] BUG: sleeping function called from invalid context at include/linux/uaccess.h:162
> [   24.176703][ T2696] in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 2696, name: trinity-c4
> [   24.177213][ T2696] preempt_count: 0, expected: 0
> [   24.177492][ T2696] no locks held by trinity-c4/2696.
> [   24.177788][ T2696] irq event stamp: 335112
> [ 24.178030][ T2696] hardirqs last enabled at (335111): irqentry_exit (kernel/entry/common.c:210) 
> [ 24.178521][ T2696] hardirqs last disabled at (335112): irqentry_enter (kernel/entry/common.c:?) 
> [ 24.179004][ T2696] softirqs last enabled at (332212): __do_softirq (kernel/softirq.c:614) 
> [ 24.179473][ T2696] softirqs last disabled at (332207): __do_softirq (kernel/softirq.c:614) 
> [   24.179948][ T2696] CPU: 1 UID: 65534 PID: 2696 Comm: trinity-c4 Tainted: G                T   6.17.0-rc2-00017-g09c737e0df5a #1 VOLUNTARY
> [   24.179952][ T2696] Tainted: [T]=RANDSTRUCT
> [   24.179954][ T2696] Call Trace:
> [ 24.179956][ T2696] __dump_stack (lib/dump_stack.c:95) 
> [ 24.179961][ T2696] dump_stack_lvl (lib/dump_stack.c:123) 
> [ 24.179963][ T2696] ? nbcon_get_cpu_emergency_nesting (kernel/printk/nbcon.c:1375) 
> [ 24.179967][ T2696] dump_stack (lib/dump_stack.c:129) 
> [ 24.179969][ T2696] __might_resched (kernel/sched/core.c:8958) 
> [ 24.179976][ T2696] __might_sleep (kernel/sched/core.c:8887) 
> [ 24.179979][ T2696] __might_fault (mm/memory.c:6957) 
> [ 24.179983][ T2696] _copy_from_user (include/linux/uaccess.h:?) 
> [ 24.179991][ T2696] insn_fetch_from_user (include/linux/uaccess.h:212 arch/x86/lib/insn-eval.c:1516) 
> [ 24.179995][ T2696] handle_invalid_op (arch/x86/kernel/traps.c:308) 
> [ 24.180010][ T2696] ? exc_overflow (arch/x86/kernel/traps.c:417) 
> [ 24.180012][ T2696] exc_invalid_op (arch/x86/kernel/traps.c:432) 
> [ 24.180014][ T2696] handle_exception (arch/x86/entry/entry_32.S:1055)

I am familiar with interrupts on microcontrollers and embedded systems,
but not with Linux's, so unsure how to proceed.

I've seen UMIP and IOPL emulation and they both run with interrupts enabled,
by means of cond_local_irq_enable, and then fetch from memory using regular
insn_fetch_from_user/get_user which may sleep.

VC, on the other hand, uses the insn_fetch_from_user_inatomic.

Can someone chime in on what should I do for this? Enable IRQs temporarily
using cond_local_irq_enable or local_irq_enable, or use the inatomic
version?