Re: [PATCH v6 bpf-next 0/5] Add support for memory-mapping BPF array maps

[Daniel Borkmann <daniel@iogearbox.net>]

On 11/17/19 6:28 PM, Andrii Nakryiko wrote:
> This patch set adds ability to memory-map BPF array maps (single- and
> multi-element). The primary use case is memory-mapping BPF array maps, created
> to back global data variables, created by libbpf implicitly. This allows for
> much better usability, along with avoiding syscalls to read or update data
> completely.
> 
> Due to memory-mapping requirements, BPF array map that is supposed to be
> memory-mapped, has to be created with special BPF_F_MMAPABLE attribute, which
> triggers slightly different memory allocation strategy internally. See
> patch 1 for details.
> 
> Libbpf is extended to detect kernel support for this flag, and if supported,
> will specify it for all global data maps automatically.
> 
> Patch #1 refactors bpf_map_inc() and converts bpf_map's refcnt to atomic64_t
> to make refcounting never fail. Patch #2 does similar refactoring for
> bpf_prog_add()/bpf_prog_inc().
> 
> v5->v6:
> - add back uref counting (Daniel);
> 
> v4->v5:
> - change bpf_prog's refcnt to atomic64_t (Daniel);
> 
> v3->v4:
> - add mmap's open() callback to fix refcounting (Johannes);
> - switch to remap_vmalloc_pages() instead of custom fault handler (Johannes);
> - converted bpf_map's refcnt/usercnt into atomic64_t;
> - provide default bpf_map_default_vmops handling open/close properly;
> 
> v2->v3:
> - change allocation strategy to avoid extra pointer dereference (Jakub);
> 
> v1->v2:
> - fix map lookup code generation for BPF_F_MMAPABLE case;
> - prevent BPF_F_MMAPABLE flag for all but plain array map type;
> - centralize ref-counting in generic bpf_map_mmap();
> - don't use uref counting (Alexei);
> - use vfree() directly;
> - print flags with %x (Song);
> - extend tests to verify bpf_map_{lookup,update}_elem() logic as well.
> 
> Andrii Nakryiko (5):
>    bpf: switch bpf_map ref counter to atomic64_t so bpf_map_inc() never
>      fails
>    bpf: convert bpf_prog refcnt to atomic64_t
>    bpf: add mmap() support for BPF_MAP_TYPE_ARRAY
>    libbpf: make global data internal arrays mmap()-able, if possible
>    selftests/bpf: add BPF_TYPE_MAP_ARRAY mmap() tests
> 

Applied, thanks!