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From:   Doug Anderson <dianders@chromium.org>
Date:   Sat, 16 May 2020 09:17:21 -0700
Message-ID: <CAD=FV=XMSsMFpPzBckkWhP6iDR4WM+qdV7J=aQCBbbBit_rDwg@mail.gmail.com>
Subject: Re: [PATCH 2/4] arm64: Extract kprobes_save_local_irqflag() and kprobes_restore_local_irqflag()
To:     "liwei (GF)" <liwei391@huawei.com>
Cc:     Daniel Thompson <daniel.thompson@linaro.org>,
        Jason Wessel <jason.wessel@windriver.com>,
        Marc Zyngier <maz@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        David Miller <davem@davemloft.net>,
        Will Deacon <will@kernel.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>, liwei1412@163.com
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Sender: linux-kernel-owner@vger.kernel.org
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Hi,

On Sat, May 16, 2020 at 1:47 AM liwei (GF) <liwei391@huawei.com> wrote:
>
> >> -               kprobes_save_local_irqflag(kcb, regs);
> >> +               kernel_prepare_single_step(&kcb->saved_irqflag, regs);
> >
> > Is there some reason to have two functions?  It seems like every time
> > you call kernel_enable_single_step() you'd want to call
> > kernel_prepare_single_step().  ...and every time you call
> > kernel_disable_single_step() you'd want to call
> > kernel_cleanup_single_step().
> >
> > Maybe you can just add the flags parameter to
> > kernel_enable_single_step() / kernel_disable_single_step() and put the
> > code in there?
> >
>
> As kernel_enable_single_step() / kernel_disable_single_step() are also called in
> breakpoint_handler() and watchpoint_handler(), i am not sure it's a right thing
> to put the daif flag prepare/cleanup into them, especially we don't have a context
> to save the flags.

I think you misunderstood what I was suggesting.  Maybe better with
examples?  I was suggesting doing this:

kcb->saved_irqflag = kernel_enable_single_step(regs);
...
kernel_disable_single_step(kcb->saved_irqflag, regs);

To me that seems better than what you have now:

kcb->saved_irqflag = kernel_prepare_single_step(regs);
kernel_enable_single_step(regs);
...
kernel_cleanup_single_step(kcb->saved_irqflag, regs);
kernel_disable_single_step();

...or am I confused?

-Doug