linux-kernel - Re: [RFC PATCH V2 4/7] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush

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Date:   Mon, 25 May 2020 21:17:32 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Lai Jiangshan <laijs@...ux.alibaba.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Alexandre Chartre <alexandre.chartre@...cle.com>
Subject: Re: [RFC PATCH V2 4/7] x86/hw_breakpoint: Prevent data breakpoints on user_pcid_flush_mask

On Mon, May 25, 2020 at 6:42 PM Lai Jiangshan <laijs@...ux.alibaba.com> wrote:
>
> The percpu user_pcid_flush_mask is used for CPU entry
> If a data breakpoint on it, it will cause an unwanted #DB.
> Protect the full cpu_tlbstate structure to be sure.
>
> There are some other percpu data used in CPU entry, but they are
> either in already-protected cpu_tss_rw or are safe to trigger #DB
> (espfix_waddr, espfix_stack).

How hard would it be to rework this to have DECLARE_PERCPU_NODEBUG()
and DEFINE_PERCPU_NODEBUG() or similar?