Re: [PATCH] mm: disable kernelcore=mirror when no mirror memory

[Mike Rapoport <rppt@kernel.org>]

On Fri, Jul 28, 2023 at 12:01:24PM +0800, Wupeng Ma wrote:
> From: Ma Wupeng <mawupeng1@huawei.com>
> 
> For system with kernelcore=mirror enabled while no mirrored memory is
> reported by efi. This could lead to kernel OOM during startup since
> all memory beside zone DMA are in the movable zone and this prevents
> the kernel to use it.
> 
> Zone DMA/DMA32 initialization is independent of mirrored memory and
> their max pfn is set in zone_sizes_init(). Since kernel can fallback
> to zone DMA/DMA32 if there is no memory in zone Normal, these zones
> are seen as mirrored memory no mather their memory attributes are.

Using kernelcore= and movablecore= always come with the risk there will be
to little memory for the kernel to use. Even if EFI reports mirrored memory
it's possible to have OOM with kernelcore=mirror because there could be
just not enough mirrored memory.
 
> To solve this problem, disable kernelcore=mirror when there is no real
> mirrored memory exists.
> 
> Signed-off-by: Ma Wupeng <mawupeng1@huawei.com>
> ---
>  mm/internal.h | 2 ++
>  mm/memblock.c | 2 +-
>  mm/mm_init.c  | 6 +++++-
>  3 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index a7d9e980429a..98a03ac74ca7 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -374,6 +374,8 @@ static inline void clear_zone_contiguous(struct zone *zone)
>  	zone->contiguous = false;
>  }
>  
> +extern bool system_has_some_mirror;
> +
>  extern int __isolate_free_page(struct page *page, unsigned int order);
>  extern void __putback_isolated_page(struct page *page, unsigned int order,
>  				    int mt);
> diff --git a/mm/memblock.c b/mm/memblock.c
> index f9e61e565a53..e7a7a65415fb 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -156,10 +156,10 @@ static __refdata struct memblock_type *memblock_memory = &memblock.memory;
>  	} while (0)
>  
>  static int memblock_debug __initdata_memblock;
> -static bool system_has_some_mirror __initdata_memblock;
>  static int memblock_can_resize __initdata_memblock;
>  static int memblock_memory_in_slab __initdata_memblock;
>  static int memblock_reserved_in_slab __initdata_memblock;
> +bool system_has_some_mirror __initdata_memblock;
>  
>  static enum memblock_flags __init_memblock choose_memblock_flags(void)
>  {
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index a1963c3322af..6267b9f75927 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -269,7 +269,11 @@ static int __init cmdline_parse_kernelcore(char *p)
>  {
>  	/* parse kernelcore=mirror */
>  	if (parse_option_str(p, "mirror")) {
> -		mirrored_kernelcore = true;
> +		if (system_has_some_mirror)
> +			mirrored_kernelcore = true;

On many architectures early parameters are parsed before memblock is setup,
so system_has_some_mirror will always be true.

> +		else
> +			pr_warn("The system has no mirror memory, disable kernelcore=mirror.\n");
> +
>  		return 0;
>  	}
>  
> -- 
> 2.25.1
> 

-- 
Sincerely yours,
Mike.