linux-kernel - Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online

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Date:   Fri, 14 Jun 2019 17:35:39 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
Cc:     Qian Cai <cai@....pw>, Dan Williams <dan.j.williams@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -next] mm/hotplug: skip bad PFNs from pfn_to_online_page()

On Fri, Jun 14, 2019 at 02:28:40PM +0530, Aneesh Kumar K.V wrote:
> Can you check with this change on ppc64.  I haven't reviewed this series yet.
> I did limited testing with change . Before merging this I need to go
> through the full series again. The vmemmap poplulate on ppc64 needs to
> handle two translation mode (hash and radix). With respect to vmemap
> hash doesn't setup a translation in the linux page table. Hence we need
> to make sure we don't try to setup a mapping for a range which is
> arleady convered by an existing mapping. 
> 
> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
> index a4e17a979e45..15c342f0a543 100644
> --- a/arch/powerpc/mm/init_64.c
> +++ b/arch/powerpc/mm/init_64.c
> @@ -88,16 +88,23 @@ static unsigned long __meminit vmemmap_section_start(unsigned long page)
>   * which overlaps this vmemmap page is initialised then this page is
>   * initialised already.
>   */
> -static int __meminit vmemmap_populated(unsigned long start, int page_size)
> +static bool __meminit vmemmap_populated(unsigned long start, int page_size)
>  {
>  	unsigned long end = start + page_size;
>  	start = (unsigned long)(pfn_to_page(vmemmap_section_start(start)));
>  
> -	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page)))
> -		if (pfn_valid(page_to_pfn((struct page *)start)))
> -			return 1;
> +	for (; start < end; start += (PAGES_PER_SECTION * sizeof(struct page))) {
>  
> -	return 0;
> +		struct mem_section *ms;
> +		unsigned long pfn = page_to_pfn((struct page *)start);
> +
> +		if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> +			return 0;

I might be missing something, but is this right?
Having a section_nr above NR_MEM_SECTIONS is invalid, but if we return 0 here,
vmemmap_populate will go on and populate it.

-- 
Oscar Salvador
SUSE L3