Re: [PATCH v2 2/2] powerpc/fadump: opt out from freeing pages on cma activation failure

[David Hildenbrand <david@redhat.com>]

On 12.01.22 20:33, Hari Bathini wrote:
> With commit a4e92ce8e4c8 ("powerpc/fadump: Reservationless firmware
> assisted dump"), Linux kernel's Contiguous Memory Allocator (CMA)
> based reservation was introduced in fadump. That change was aimed at
> using CMA to let applications utilize the memory reserved for fadump
> while blocking it from being used for kernel pages. The assumption
> was, even if CMA activation fails for whatever reason, the memory
> still remains reserved to avoid it from being used for kernel pages.
> But commit 072355c1cf2d ("mm/cma: expose all pages to the buddy if
> activation of an area fails") breaks this assumption as it started
> exposing all pages to buddy allocator on CMA activation failure.
> It led to warning messages like below while running crash-utility
> on vmcore of a kernel having above two commits:
> 
>   crash: seek error: kernel virtual address: <from reserved region>
> 
> To fix this problem, opt out from exposing pages to buddy allocator
> on CMA activation failure for fadump reserved memory.
> 
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---
>  arch/powerpc/kernel/fadump.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/arch/powerpc/kernel/fadump.c b/arch/powerpc/kernel/fadump.c
> index b7ceb041743c..82058b52e34a 100644
> --- a/arch/powerpc/kernel/fadump.c
> +++ b/arch/powerpc/kernel/fadump.c
> @@ -112,6 +112,12 @@ static int __init fadump_cma_init(void)
>  		return 1;
>  	}
>  
> +	/*
> +	 *  If CMA activation fails, keep the pages reserved, instead of
> +	 *  exposing them to buddy allocator. Same as 'fadump=nocma' case.
> +	 */
> +	cma_reserve_pages_on_error(fadump_cma);
> +
>  	/*
>  	 * So we now have successfully initialized cma area for fadump.
>  	 */

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Thanks,

David / dhildenb