Re: [PATCH bpf-next v1 2/8] bpf: Add bpf_page_to_pfn helper

[Yonghong Song <yhs@fb.com>]

On 11/15/21 9:42 PM, Kumar Kartikeya Dwivedi wrote:
> In CRIU, we need to be able to determine whether the page pinned by
> io_uring is still present in the same range in the process VMA.
> /proc/<pid>/pagemap gives us the PFN, hence using this helper we can
> establish this mapping easily from the iterator side.
> 
> It is a simple wrapper over the in-kernel page_to_pfn helper, and
> ensures the passed in pointer is a struct page PTR_TO_BTF_ID. This is
> obtained from the bvec of io_uring_ubuf for the CRIU usecase.
> 
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
> ---
>   fs/io_uring.c                  | 17 +++++++++++++++++
>   include/linux/bpf.h            |  1 +
>   include/uapi/linux/bpf.h       |  9 +++++++++
>   kernel/trace/bpf_trace.c       |  2 ++
>   scripts/bpf_doc.py             |  2 ++
>   tools/include/uapi/linux/bpf.h |  9 +++++++++
>   6 files changed, 40 insertions(+)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 46a110989155..9e9df6767e29 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -11295,6 +11295,23 @@ static struct bpf_iter_reg io_uring_buf_reg_info = {
>   	.seq_info	   = &bpf_io_uring_buf_seq_info,
>   };
>   
> +BPF_CALL_1(bpf_page_to_pfn, struct page *, page)
> +{
> +	/* PTR_TO_BTF_ID can be NULL */
> +	if (!page)
> +		return U64_MAX;
> +	return page_to_pfn(page);
> +}
> +
> +BTF_ID_LIST_SINGLE(btf_page_to_pfn_ids, struct, page)
> +
> +const struct bpf_func_proto bpf_page_to_pfn_proto = {
> +	.func		= bpf_page_to_pfn,
> +	.ret_type	= RET_INTEGER,
> +	.arg1_type	= ARG_PTR_TO_BTF_ID,
> +	.arg1_btf_id	= &btf_page_to_pfn_ids[0],

Does this helper need to be gpl_only?

> +};
> +
>   static int __init io_uring_iter_init(void)
>   {
>   	io_uring_buf_reg_info.ctx_arg_info[0].btf_id = btf_io_uring_ids[0];
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