netdev - Re: [PATCH bpf-next] bpf: use kvmalloc in map_lookup

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Message-ID: <1b3cb059-9ecb-a0c9-3c99-805788088d09@iogearbox.net>
Date:   Mon, 16 Aug 2021 23:43:21 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Stanislav Fomichev <sdf@...gle.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     ast@...nel.org, andrii@...nel.org
Subject: Re: [PATCH bpf-next] bpf: use kvmalloc in map_lookup_elem

On 8/16/21 6:48 PM, Stanislav Fomichev wrote:
> Use kvmalloc/kvfree for temporary value when looking up a map.
> kmalloc might not be sufficient for percpu maps where the value is big.
> 
> Can be reproduced with netcnt test on qemu with "-smp 255".
> 
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>
> ---
>   kernel/bpf/syscall.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
> index 9a2068e39d23..ae0b1c1c8ece 100644
> --- a/kernel/bpf/syscall.c
> +++ b/kernel/bpf/syscall.c
> @@ -1076,7 +1076,7 @@ static int map_lookup_elem(union bpf_attr *attr)
>   	value_size = bpf_map_value_size(map);
>   
>   	err = -ENOMEM;
> -	value = kmalloc(value_size, GFP_USER | __GFP_NOWARN);
> +	value = kvmalloc(value_size, GFP_USER | __GFP_NOWARN);
>   	if (!value)
>   		goto free_key;

What about other cases like map_update_elem(), shouldn't they be adapted
similarly?

Thanks,
Daniel