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Date:   Sat, 23 Nov 2019 22:15:06 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Andrii Nakryiko <andriin@...com>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, ast@...com
Cc:     andrii.nakryiko@...il.com, kernel-team@...com,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH bpf-next] bpf: fail mmap without CONFIG_MMU

On 11/23/19 9:56 PM, Andrii Nakryiko wrote:
> mmap() support for BPF array depends on vmalloc_user_node_flags, which is
> available only on CONFIG_MMU configurations. Fail mmap-able allocations if no
> CONFIG_MMU is set.
> 
> Cc: Johannes Weiner <hannes@...xchg.org>
> Reported-by: kbuild test robot <lkp@...el.com>
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>   kernel/bpf/syscall.c | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index bb002f15b32a..242a06fbdf18 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -156,8 +156,12 @@ static void *__bpf_map_area_alloc(u64 size, int numa_node, bool mmapable)
>   	}
>   	if (mmapable) {
>   		BUG_ON(!PAGE_ALIGNED(size));
> +#ifndef CONFIG_MMU
> +		return NULL;
> +#else
>   		return vmalloc_user_node_flags(size, numa_node, GFP_KERNEL |
>   					       __GFP_RETRY_MAYFAIL | flags);

Hmm, this should rather live in include/linux/vmalloc.h, otherwise every future
user of vmalloc_user_node_flags() would need to add this ifdef? vmalloc.h has
the below, so perhaps this could be added there instead:

[..]
#ifndef CONFIG_MMU
extern void *__vmalloc_node_flags(unsigned long size, int node, gfp_t flags);
static inline void *__vmalloc_node_flags_caller(unsigned long size, int node,
                                                 gfp_t flags, void *caller)
{
         return __vmalloc_node_flags(size, node, flags);
}
#else
extern void *__vmalloc_node_flags_caller(unsigned long size,
                                          int node, gfp_t flags, void *caller);
#endif
[..]

> +#endif
>   	}
>   	return __vmalloc_node_flags_caller(size, numa_node,
>   					   GFP_KERNEL | __GFP_RETRY_MAYFAIL |
> 

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