linux-kernel - Re: [PATCH v4] x86/gart/kcore: Exclude GART aperture from kcore

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Date:   Wed, 6 Mar 2019 18:03:46 +0100
From:   Jiri Bohac <jbohac@...e.cz>
To:     Kairui Song <kasong@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Omar Sandoval <osandov@...com>, Baoquan He <bhe@...hat.com>,
        Dave Young <dyoung@...hat.com>
Subject: Re: [PATCH v4] x86/gart/kcore: Exclude GART aperture from kcore

Hi,

On Wed, Mar 06, 2019 at 07:38:59PM +0800, Kairui Song wrote:
> +int register_mem_pfn_is_ram(int (*fn)(unsigned long pfn))
> +{
> +	if (mem_pfn_is_ram)
> +		return -EBUSY;
> +	mem_pfn_is_ram = fn;
> +	return 0;
> +}
> +
> +void unregister_mem_pfn_is_ram(void)
> +{
> +	mem_pfn_is_ram = NULL;
> +}
> +
> +static int pfn_is_ram(unsigned long pfn)
> +{
> +	if (mem_pfn_is_ram)
> +		return mem_pfn_is_ram(pfn);
> +	else
> +		return 1;
> +}
> +

If anyone were ever to use unregister_mem_pfn_is_ram(),
pfn_is_ram() would become racy.

In V2 you had this:
	+       fn = mem_pfn_is_ram;
	+       if (fn)
	+               ret = fn(pfn);

I agree it's unnecessary since nothing uses
unregister_mem_pfn_is_ram(). But then I think it would be best to
just drop the unregister function.

Otherwise the patch looks good to me.

-- 
Jiri Bohac <jbohac@...e.cz>
SUSE Labs, Prague, Czechia