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Subject: Re: [PATCH] memblock: Check memory add/cap ordering
To:     Geert Uytterhoeven <geert+renesas@glider.be>,
        Mike Rapoport <rppt@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
References: <aabc5bad008d49f07d542815c6c8d28ec90bb09e.1628672091.git.geert+renesas@glider.be>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
Message-ID: <1c4cb6e9-2ca9-9738-9706-28ff94f8fdcc@redhat.com>
Date:   Wed, 11 Aug 2021 11:35:33 +0200
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On 11.08.21 10:55, Geert Uytterhoeven wrote:
> For memblock_cap_memory_range() to work properly, it should be called
> after memory is detected and added to memblock with memblock_add() or
> memblock_add_node().  If memblock_cap_memory_range() would be called
> before memory is registered, we may silently corrupt memory later
> because the crash kernel will see all memory as available.
> 
> Print a warning and bail out if ordering is not satisfied.
> 
> Suggested-by: Mike Rapoport <rppt@kernel.org>
> Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> ---
>   mm/memblock.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 57a9849a5d820c34..e2ca8ddc8ebebf4e 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -1685,6 +1685,11 @@ void __init memblock_cap_memory_range(phys_addr_t base, phys_addr_t size)
>   	if (!size)
>   		return;
>   
> +	if (memblock.memory.cnt <= 1) {
> +		pr_warn("%s: No memory registered yet\n", __func__);
> +		return;
> +	}
> +
>   	ret = memblock_isolate_range(&memblock.memory, base, size,
>   						&start_rgn, &end_rgn);
>   	if (ret)
> 

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

-- 
Thanks,

David / dhildenb