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From: Thomas Gleixner <tglx@linutronix.de>
To: Kees Cook <keescook@chromium.org>, linux-kernel@vger.kernel.org
In-Reply-To: <20200603233203.1695403-2-keescook@chromium.org>
Date: Thu, 04 Jun 2020 09:58:07 +0200
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Cc: Andy Whitcroft <apw@canonical.com>, Kees Cook <keescook@chromium.org>,
	linux-ide@vger.kernel.org, netdev@vger.kernel.org,
	x86@kernel.org, linux-wireless@vger.kernel.org,
	linux-spi@vger.kernel.org, linux-block@vger.kernel.org,
	Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
	linux-mm@kvack.org, Alexander Potapenko <glider@google.com>,
	b43-dev@lists.infradead.org, clang-built-linux@googlegroups.com,
	Joe Perches <joe@perches.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	linux-clk@vger.kernel.org, drbd-dev@lists.linbit.com
Subject: Re: [Drbd-dev] [PATCH 01/10] x86/mm/numa: Remove
	uninitialized_var() usage
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Kees Cook <keescook@chromium.org> writes:
> -#ifdef NODE_NOT_IN_PAGE_FLAGS
> -	pfn_align = node_map_pfn_alignment();
> -	if (pfn_align && pfn_align < PAGES_PER_SECTION) {
> -		printk(KERN_WARNING "Node alignment %LuMB < min %LuMB, rejecting NUMA config\n",
> -		       PFN_PHYS(pfn_align) >> 20,
> -		       PFN_PHYS(PAGES_PER_SECTION) >> 20);
> -		return -EINVAL;
> +	if (IS_ENABLED(NODE_NOT_IN_PAGE_FLAGS)) {

Hrm, clever ...

> +		unsigned long pfn_align = node_map_pfn_alignment();
> +
> +		if (pfn_align && pfn_align < PAGES_PER_SECTION) {
> +			pr_warn("Node alignment %LuMB < min %LuMB, rejecting NUMA config\n",
> +				PFN_PHYS(pfn_align) >> 20,
> +				PFN_PHYS(PAGES_PER_SECTION) >> 20);
> +			return -EINVAL;
> +		}
>  	}
> -#endif
>  	if (!numa_meminfo_cover_memory(mi))
>  		return -EINVAL;
>  
> diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
> index 71283739ffd2..1a4cdec2bd29 100644
> --- a/include/linux/page-flags-layout.h
> +++ b/include/linux/page-flags-layout.h
> @@ -100,7 +100,7 @@
>   * there.  This includes the case where there is no node, so it is implicit.
>   */
>  #if !(NODES_WIDTH > 0 || NODES_SHIFT == 0)
> -#define NODE_NOT_IN_PAGE_FLAGS
> +#define NODE_NOT_IN_PAGE_FLAGS 1

but if we ever lose the 1 then the above will silently compile the code
within the IS_ENABLED() section out.

Thanks,

        tglx