On Fri, Nov 19, 2021 at 12:48:39AM IST, Yonghong Song wrote:

On 11/18/21 10:30 AM, Kumar Kartikeya Dwivedi wrote:

quoted

On Thu, Nov 18, 2021 at 10:57:15PM IST, Yonghong Song wrote:

quoted

On 11/15/21 9:42 PM, Kumar Kartikeya Dwivedi wrote:

quoted

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?

The typically guideline whether the same info can be retrieved from
userspace. If yes, no gpl is needed. Otherwe, it needs to be gpl.

I think it can already be obtained using /proc/<PID>/pagemap, so not needed.

Also, the helper is implemented in io_uring.c and the helper
is used by tracing programs. Maybe we can put the helper
in bpf_trace.c? The helper itself is not tied to io_uring, right?

Right, I'll move it outside CONFIG_IO_URING in v2. That's also why the build
failed on this patch.

--
Kartikeya