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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: yhchen312@gmail.com
Cc: anup@brainfault.org, atish.patra@linux.dev, pjw@kernel.org,
	palmer@dabbelt.com, aou@eecs.berkeley.edu, alex@ghiti.fr,
	clrkwllms@kernel.org, rostedt@goodmis.org, kvm@vger.kernel.org,
	kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev,
	Quan Zhou <zhouquan@iscas.ac.cn>
Subject: Re: [PATCH] RISC-V: KVM: Use raw_spinlock for VMID update critical
 section
Message-ID: <20260717065137.FQ5Ax2W-@linutronix.de>
References: <20260716064011.2387501-1-yhchen312@gmail.com>
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In-Reply-To: <20260716064011.2387501-1-yhchen312@gmail.com>

On 2026-07-16 14:40:11 [+0800], yhchen312@gmail.com wrote:
> From: "Yuhang.chen" <yhchen312@gmail.com>
> 
> The VMID update critical section performs an IPI broadcast via
> on_each_cpu_mask() on VMID version rollover, which must not be preempted
> under PREEMPT_RT.

Here you state _why_ it must not be preempted. What would be the worst
that could happen.

>                   Convert vmid_lock to raw_spinlock_t and use plain
That part starting with "Convert" belongs into into a new line.

> raw_spin_lock()/raw_spin_unlock() (interrupts stay enabled, since
> on_each_cpu_mask() requires it).
> 
> Assisted-by: YuanSheng:deepseek-v4-pro
> Co-developed-by: Quan Zhou <zhouquan@iscas.ac.cn>
> Signed-off-by: Quan Zhou <zhouquan@iscas.ac.cn>
> Signed-off-by: Yuhang.chen <yhchen312@gmail.com>

Sebastian