linux-kernel - Re: [PATCHv2 6/7] x86/mm: remove bottom-up allocation style for x86

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Date:   Mon, 14 Jan 2019 15:27:25 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Pingfan Liu <kernelfans@...il.com>, linux-kernel@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Yinghai Lu <yinghai@...nel.org>,
        Tejun Heo <tj@...nel.org>, Chao Fan <fanc.fnst@...fujitsu.com>,
        Baoquan He <bhe@...hat.com>, Juergen Gross <jgross@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Michal Hocko <mhocko@...e.com>, x86@...nel.org,
        linux-acpi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 6/7] x86/mm: remove bottom-up allocation style for
 x86_64

On 1/10/19 9:12 PM, Pingfan Liu wrote:
> Although kaslr-kernel can avoid to stain the movable node. [1]

Can you explain what staining is, or perhaps try to use some more
standard nomenclature?  There are exactly 0 instances of the word
"stain" in arch/x86/ or mm/.

> But the
> pgtable can still stain the movable node. That is a probability problem,
> although low, but exist. This patch tries to make it certainty by
> allocating pgtable on unmovable node, instead of following kernel end.

Anyway, can you read my suggested summary in the earlier patch and see
if it fits or if I missed anything?  This description is really hard to
read.

...> +#ifdef CONFIG_X86_32
> +
> +static unsigned long min_pfn_mapped;
> +
>  static unsigned long __init get_new_step_size(unsigned long step_size)
>  {
>  	/*
> @@ -653,6 +655,32 @@ static void __init memory_map_bottom_up(unsigned long map_start,
>  	}
>  }
>  
> +static unsigned long __init init_range_memory_mapping32(
> +	unsigned long r_start, unsigned long r_end)
> +{

Why is this returning a value which is not used?

Did you compile this?  Didn't you get a warning that you're not
returning a value from a function returning non-void?

Also, I'd much rather see something like this written:

static __init
unsigned long init_range_memory_mapping32(unsigned long r_start,
					  unsigned long r_end)

than what you have above.  But, if you get rid of the 'unsigned long',
it will look much more sane in the first place.