On Mon, Dec 07, 2020 at 05:41:05PM -0800, Yonghong Song wrote:
>
>
> On 12/7/20 8:07 AM, Brendan Jackman wrote:
> > The BPF_FETCH field can be set in bpf_insn.imm, for BPF_ATOMIC
> > instructions, in order to have the previous value of the
> > atomically-modified memory location loaded into the src register
> > after an atomic op is carried out.
> >
> > Suggested-by: Yonghong Song <yhs@xxxxxx>
> > Signed-off-by: Brendan Jackman <jackmanb@xxxxxxxxxx>
> > ---
> > arch/x86/net/bpf_jit_comp.c | 4 ++++
> > include/linux/filter.h | 1 +
> > include/uapi/linux/bpf.h | 3 +++
> > kernel/bpf/core.c | 13 +++++++++++++
> > kernel/bpf/disasm.c | 7 +++++++
> > kernel/bpf/verifier.c | 33 ++++++++++++++++++++++++---------
> > tools/include/linux/filter.h | 11 +++++++++++
> > tools/include/uapi/linux/bpf.h | 3 +++
> > 8 files changed, 66 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
> [...]
>
> > index f345f12c1ff8..4e0100ba52c2 100644
> > --- a/tools/include/linux/filter.h
> > +++ b/tools/include/linux/filter.h
> > @@ -173,6 +173,7 @@
> > * Atomic operations:
> > *
> > * BPF_ADD *(uint *) (dst_reg + off16) += src_reg
> > + * BPF_ADD | BPF_FETCH src_reg = atomic_fetch_add(dst_reg + off16, src_reg);
> > */
> > #define BPF_ATOMIC64(OP, DST, SRC, OFF) \
> > @@ -201,6 +202,16 @@
> > .off = OFF, \
> > .imm = BPF_ADD })
> > +/* Atomic memory add with fetch, src_reg = atomic_fetch_add(dst_reg + off, src_reg); */
> > +
> > +#define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \
> > + ((struct bpf_insn) { \
> > + .code = BPF_STX | BPF_SIZE(SIZE) | BPF_ATOMIC, \
> > + .dst_reg = DST, \
> > + .src_reg = SRC, \
> > + .off = OFF, \
> > + .imm = BPF_ADD | BPF_FETCH })
>
> Not sure whether it is a good idea or not to fold this into BPF_ATOMIC
> macro. At least you can define BPF_ATOMIC macro and
> #define BPF_ATOMIC_FETCH_ADD(SIZE, DST, SRC, OFF) \
> BPF_ATOMIC(SIZE, DST, SRC, OFF, BPF_ADD | BPF_FETCH)
>
> to avoid too many code duplications?
Oops.. I intended to totally get rid these and folded them into
BPF_ATOMIC{64,32}! OK, let's combine all of them into a single macro.
It will have to be called something slightly awkward like
BPF_ATOMIC_INSN because BPF_ATOMIC is the name of the BPF_OP.
>
> > +
> > /* Memory store, *(uint *) (dst_reg + off16) = imm32 */
> > #define BPF_ST_MEM(SIZE, DST, OFF, IMM) \
> > diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
> > index 98161e2d389f..d5389119291e 100644
> > --- a/tools/include/uapi/linux/bpf.h
> > +++ b/tools/include/uapi/linux/bpf.h
> > @@ -44,6 +44,9 @@
> > #define BPF_CALL 0x80 /* function call */
> > #define BPF_EXIT 0x90 /* function return */
> > +/* atomic op type fields (stored in immediate) */
> > +#define BPF_FETCH 0x01 /* fetch previous value into src reg */
> > +
> > /* Register numbers */
> > enum {
> > BPF_REG_0 = 0,
> >
