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From:   Doug Anderson <dianders@chromium.org>
Date:   Fri, 1 May 2020 11:15:33 -0700
Message-ID: <CAD=FV=WrdKRfM5ExJnhJBCn1ZBTAviuOSq+judda8YSiwbkREw@mail.gmail.com>
Subject: Re: [PATCH] arm64: cacheflush: Fix KGDB trap detection
To:     Daniel Thompson <daniel.thompson@linaro.org>
Cc:     Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Jason Wessel <jason.wessel@windriver.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Patch Tracking <patches@linaro.org>
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Hi,

On Fri, May 1, 2020 at 9:20 AM Daniel Thompson
<daniel.thompson@linaro.org> wrote:
>
> flush_icache_range() contains a bodge to avoid issuing IPIs when the kgdb
> trap handler is running because issuing IPIs is unsafe (and unnecessary)
> in this exection context. However the current test is flawed: it both

s/exection/execution/

> over-matches (could skip the IPI when the kgdb trap is not running) and
> under-matches (does not skip the IPI for all kgdb cache operations).

Maybe explain why?  I believe this is because "kgdb_connected"
signifies that a host "gdb" is connected.

* If we're sitting at the kdb prompt "kgdb_connected" won't be set but
we might still try to do something with a breakpoint with interrupts
off.

* If we are currently _not_ stopped in the debugger but the host "gdb"
is connected then "kgdb_connected" will continue to be set.  In this
context we will exit early if any other callers happen to try to cache
flush with interrupts disabled.


> Fix by replacing the ad-hoc check with the proper kgdb macro. This also
> allows us to drop the #ifdef wrapper.
>
> Fixes: 3b8c9f1cdfc5 ("arm64: IPI each CPU after invalidating the I-cache for kernel mappings")
> Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
> ---
>  arch/arm64/include/asm/cacheflush.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)

Other than the suggestions to the commit message:

Reviewed-by: Douglas Anderson <dianders@chromium.org>