linux-kernel - Re: [PATCH 13/13] kdb: Add mdi, mdiW / mdiWcN commands to show iomapped memory

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Date: Tue, 18 Jun 2024 16:59:38 +0100
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Douglas Anderson <dianders@...omium.org>
Cc: kgdb-bugreport@...ts.sourceforge.net,
	Christophe JAILLET <christophe.jaillet@...adoo.fr>,
	Jason Wessel <jason.wessel@...driver.com>,
	Thorsten Blum <thorsten.blum@...lux.com>,
	Yuran Pereira <yuran.pereira@...mail.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 13/13] kdb: Add mdi, mdiW / mdiWcN commands to show
 iomapped memory

On Mon, Jun 17, 2024 at 05:34:47PM -0700, Douglas Anderson wrote:
> Add commands that are like the other "md" commands but that allow you
> to read memory that's in the IO space.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>

Sorry to be the bearer of bad news but...


> ---
> <snip>
> +/*
> + * kdb_getioword
> + * Inputs:
> + *	word	Pointer to the word to receive the result.
> + *	addr	Address of the area to copy.
> + *	size	Size of the area.
> + * Returns:
> + *	0 for success, < 0 for error.
> + */
> +int kdb_getioword(unsigned long *word, unsigned long addr, size_t size)
> +{
> +	void __iomem *mapped = ioremap(addr, size);

ioremap() is a might_sleep() function. It's unsafe to call it from the
debug trap handler.

I'm afraid I don't know a safe alternative either. Machinary such as
kmap_atomic() needs a page and iomem won't have one.


Daniel.