linux-kernel - Re: [PATCH v2 1/2] mm: memblock: enforce overlap of memory.memblock and memory.reserved

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Date:   Mon, 14 Dec 2020 11:11:35 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrea Arcangeli <aarcange@...hat.com>,
        Baoquan He <bhe@...hat.com>, Mel Gorman <mgorman@...e.de>,
        Michal Hocko <mhocko@...nel.org>,
        Mike Rapoport <rppt@...ux.ibm.com>, Qian Cai <cai@....pw>,
        Vlastimil Babka <vbabka@...e.cz>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, stable@...r.kernel.org,
        Dan Williams <dan.j.williams@...el.com>
Subject: Re: [PATCH v2 1/2] mm: memblock: enforce overlap of memory.memblock
 and memory.reserved

On 09.12.20 22:43, Mike Rapoport wrote:
> From: Mike Rapoport <rppt@...ux.ibm.com>
> 
> memblock does not require that the reserved memory ranges will be a subset
> of memblock.memory.
> 
> As the result there maybe reserved pages that are not in the range of any
> zone or node because zone and node boundaries are detected based on
> memblock.memory and pages that only present in memblock.reserved are not
> taken into account during zone/node size detection.
> 
> Make sure that all ranges in memblock.reserved are added to memblock.memory
> before calculating node and zone boundaries.
> 
> Fixes: 73a6e474cb37 ("mm: memmap_init: iterate over memblock regions rather that check each PFN")
> Reported-by: Andrea Arcangeli <aarcange@...hat.com>
> Signed-off-by: Mike Rapoport <rppt@...ux.ibm.com>
> ---
>  include/linux/memblock.h |  1 +
>  mm/memblock.c            | 24 ++++++++++++++++++++++++
>  mm/page_alloc.c          |  7 +++++++
>  3 files changed, 32 insertions(+)
> 
> diff --git a/include/linux/memblock.h b/include/linux/memblock.h
> index ef131255cedc..e64dae2dd1ce 100644
> --- a/include/linux/memblock.h
> +++ b/include/linux/memblock.h
> @@ -120,6 +120,7 @@ int memblock_clear_nomap(phys_addr_t base, phys_addr_t size);
>  unsigned long memblock_free_all(void);
>  void reset_node_managed_pages(pg_data_t *pgdat);
>  void reset_all_zones_managed_pages(void);
> +void memblock_enforce_memory_reserved_overlap(void);
>  
>  /* Low level functions */
>  void __next_mem_range(u64 *idx, int nid, enum memblock_flags flags,
> diff --git a/mm/memblock.c b/mm/memblock.c
> index b68ee86788af..9277aca642b2 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1857,6 +1857,30 @@ void __init_memblock memblock_trim_memory(phys_addr_t align)
>  	}
>  }
>  
> +/**
> + * memblock_enforce_memory_reserved_overlap - make sure every range in
> + * @memblock.reserved is covered by @memblock.memory
> + *
> + * The data in @memblock.memory is used to detect zone and node boundaries
> + * during initialization of the memory map and the page allocator. Make
> + * sure that every memory range present in @memblock.reserved is also added
> + * to @memblock.memory even if the architecture specific memory
> + * initialization failed to do so
> + */
> +void __init memblock_enforce_memory_reserved_overlap(void)
> +{
> +	phys_addr_t start, end;
> +	int nid;
> +	u64 i;
> +
> +	__for_each_mem_range(i, &memblock.reserved, &memblock.memory,
> +			     NUMA_NO_NODE, MEMBLOCK_NONE, &start, &end, &nid) {
> +		pr_warn("memblock: reserved range [%pa-%pa] is not in memory\n",
> +			&start, &end);
> +		memblock_add_node(start, (end - start), nid);
> +	}
> +}
> +
>  void __init_memblock memblock_set_current_limit(phys_addr_t limit)
>  {
>  	memblock.current_limit = limit;
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index eaa227a479e4..dbc57dbbacd8 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7436,6 +7436,13 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>  	memset(arch_zone_highest_possible_pfn, 0,
>  				sizeof(arch_zone_highest_possible_pfn));
>  
> +	/*
> +	 * Some architectures (e.g. x86) have reserved pages outside of
> +	 * memblock.memory. Make sure these pages are taken into account
> +	 * when detecting zone and node boundaries
> +	 */
> +	memblock_enforce_memory_reserved_overlap();
> +
>  	start_pfn = find_min_pfn_with_active_regions();
>  	descending = arch_has_descending_max_zone_pfns();
>  
> 

CCing Dan.

This implies that any memory that is E820_TYPE_SOFT_RESERVED that was
reserved via memblock_reserve() will be added via memblock_add_node() as
well, resulting in all such memory getting a memmap allocated right when
booting up, right?

IIRC, there are use cases where that is absolutely not desired.

Am I missing something? (@Dan?)

-- 
Thanks,

David / dhildenb