On Wed, Feb 7, 2024 at 5:33 AM Barret Rhoden <brho@xxxxxxxxxx> wrote:
>
>
> if i knew userspace wasn't going to follow pointers, NO_USER_CONV would
> both be a speedup and make it so i don't have to worry about mmapping to
> the same virtual address in every process that shares the arena map.
> though this latter feature isn't in the code. right now you have to
> have it mmapped at the same user_va in all address spaces. that's not a
> huge deal for me either way.
Not quite. With:
struct {
__uint(type, BPF_MAP_TYPE_ARENA);
...
__ulong(map_extra, 2ull << 44); /* start of mmap() region */
...
} arena SEC(".maps");
the future user_vm_start will be specified at map creation time,
so arena doesn't have to be mapped to be usable.
But having an address known early helps potential future mmap-s.
Like to examine the state of the arena with bpftool.
