linux-kernel - Re: mm: Use phys_addr_t for reserve_bootmem

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Message-ID: <573B273D.9040201@canonical.com>
Date:	Tue, 17 May 2016 16:14:21 +0200
From:	Stefan Bader <stefan.bader@...onical.com>
To:	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:	kernel-team@...ts.ubuntu.com, Mel Gorman <mgorman@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: mm: Use phys_addr_t for reserve_bootmem_region arguments

On 17.05.2016 15:20, Stefan Bader wrote:
> Re-posting to a hopefully better suited audience. I hit this problem
> when trying to boot a i386 dom0 (PAE enabled) on a 64bit Xen host using
> a config which would result in a reserved memory range starting at 4MB.

Of course that ^ should be "starting at 4GB" not MB...

> Due to the usage of unsigned long as arguments for start address and
> length, this would wrap and actually mark the lower memory range staring
> from 0 as reserved. Between kernel version 4.2 and 4.4 this somehow boots
> but starting with 4.4 the result is a panic and reboot.
> 
> Not sure this special Xen case is the only one affected, but in general
> it seems more correct to use phys_addr_t as the type for start and end
> as that is the type used in the memblock region definitions and those
> are 64bit (at least with PAE enabled).
> 
> -Stefan
> 
> 
> 
> From 1588a8b3983f63f8e690b91e99fe631902e38805 Mon Sep 17 00:00:00 2001
> From: Stefan Bader <stefan.bader@...onical.com>
> Date: Tue, 10 May 2016 19:05:16 +0200
> Subject: [PATCH] mm: Use phys_addr_t for reserve_bootmem_region arguments
> 
> Since 92923ca the reserved bit is set on reserved memblock regions.
> However start and end address are passed as unsigned long. This is
> only 32bit on i386, so it can end up marking the wrong pages reserved
> for ranges at 4GB and above.
> 
> This was observed on a 32bit Xen dom0 which was booted with initial
> memory set to a value below 4G but allowing to balloon in memory
> (dom0_mem=1024M for example). This would define a reserved bootmem
> region for the additional memory (for example on a 8GB system there was
> a reverved region covering the 4GB-8GB range). But since the addresses
> were passed on as unsigned long, this was actually marking all pages
> from 0 to 4GB as reserved.
> 
> Fixes: 92923ca "mm: meminit: only set page reserved in the memblock region"
> Signed-off-by: Stefan Bader <stefan.bader@...onical.com>
> Cc: <stable@...nel.org> # 4.2+
> ---
>  include/linux/mm.h | 2 +-
>  mm/page_alloc.c    | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index b56ff72..4c1ff62 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -1715,7 +1715,7 @@ extern void free_highmem_page(struct page *page);
>  extern void adjust_managed_page_count(struct page *page, long count);
>  extern void mem_init_print_info(const char *str);
>  
> -extern void reserve_bootmem_region(unsigned long start, unsigned long end);
> +extern void reserve_bootmem_region(phys_addr_t start, phys_addr_t end);
>  
>  /* Free the reserved page into the buddy system, so it gets managed. */
>  static inline void __free_reserved_page(struct page *page)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index c69531a..eb66f89 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -951,7 +951,7 @@ static inline void init_reserved_page(unsigned long pfn)
>   * marks the pages PageReserved. The remaining valid pages are later
>   * sent to the buddy page allocator.
>   */
> -void __meminit reserve_bootmem_region(unsigned long start, unsigned long end)
> +void __meminit reserve_bootmem_region(phys_addr_t start, phys_addr_t end)
>  {
>  	unsigned long start_pfn = PFN_DOWN(start);
>  	unsigned long end_pfn = PFN_UP(end);
> 



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