linux-kernel - Re: Why do kprobes and uprobes singlestep?

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Message-ID: <20210302203134.GC21871@redhat.com>
Date:   Tue, 2 Mar 2021 21:31:34 +0100
From:   Oleg Nesterov <oleg@...hat.com>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>, X86 ML <x86@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Subject: Re: Why do kprobes and uprobes singlestep?

On 03/02, Masami Hiramatsu wrote:
>
> > Not sure I understand you correctly, I know almost nothing about low-level
> > x86  magic.
>
> x86 has normal interrupt and NMI. When an NMI occurs the CPU masks NMI
> (the mask itself is hidden status) and IRET releases the mask. The problem
> is that if an INT3 is hit in the NMI handler and does a single-stepping,
> it has to use IRET for atomically setting TF and return.

Ah, thanks a lot,

Oleg.