> On Nov 7, 2019, at 2:55 PM, Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> wrote:
>
> On Thu, Nov 07, 2019 at 10:37:19PM +0000, Song Liu wrote:
>>
>>
>>> On Nov 6, 2019, at 9:46 PM, Alexei Starovoitov <ast@xxxxxxxxxx> wrote:
>>>
>>
>> [...]
>>
>>>
>>> Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx>
>>> Acked-by: Andrii Nakryiko <andriin@xxxxxx>
>>> ---
>>> arch/x86/net/bpf_jit_comp.c | 227 ++++++++++++++++++++++++++++++--
>>> include/linux/bpf.h | 98 ++++++++++++++
>>> include/uapi/linux/bpf.h | 2 +
>>> kernel/bpf/Makefile | 1 +
>>> kernel/bpf/btf.c | 77 ++++++++++-
>>> kernel/bpf/core.c | 1 +
>>> kernel/bpf/syscall.c | 53 +++++++-
>>> kernel/bpf/trampoline.c | 252 ++++++++++++++++++++++++++++++++++++
>>> kernel/bpf/verifier.c | 39 ++++++
>>> 9 files changed, 732 insertions(+), 18 deletions(-)
>>> create mode 100644 kernel/bpf/trampoline.c
>>>
>>> diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
>>> index 8631d3bd637f..44169e8bffc0 100644
>>> --- a/arch/x86/net/bpf_jit_comp.c
>>> +++ b/arch/x86/net/bpf_jit_comp.c
>>> @@ -98,6 +98,7 @@ static int bpf_size_to_x86_bytes(int bpf_size)
>>>
>>> /* Pick a register outside of BPF range for JIT internal work */
>>> #define AUX_REG (MAX_BPF_JIT_REG + 1)
>>> +#define X86_REG_R9 (MAX_BPF_JIT_REG + 2)
>>>
>>> /*
>>> * The following table maps BPF registers to x86-64 registers.
>>> @@ -123,6 +124,7 @@ static const int reg2hex[] = {
>>> [BPF_REG_FP] = 5, /* RBP readonly */
>>> [BPF_REG_AX] = 2, /* R10 temp register */
>>> [AUX_REG] = 3, /* R11 temp register */
>>> + [X86_REG_R9] = 1, /* R9 register, 6th function argument */
>>
>> We should update the comment above this:
>>
>> * Also x86-64 register R9 is unused. ...
>
> good point. fixed.
>
>>> + /* One half of the page has active running trampoline.
>>> + * Another half is an area for next trampoline.
>>> + * Make sure the trampoline generation logic doesn't overflow.
>>> + */
>>> + if (WARN_ON_ONCE(prog - (u8 *)image > PAGE_SIZE / 2 - BPF_INSN_SAFETY))
>>> + return -EFAULT;
>>
>> Given max number of args, can we catch this error at compile time?
>
> I don't see how to do that. I was thinking about having fake __init function
> that would call it with flags that can generate the longest trampoline, but
> it's not fool proof either.
> So I've added a test for it instead. See patch 10.
>
>>> +
>>> +static int bpf_trampoline_update(struct bpf_prog *prog)
>>
>> Seems argument "prog" is not used at all?
>
> like one below ? ;)
e... I was really dumb... sorry..
Maybe we should just pass the tr in?
>
>>> +{
>>> + struct bpf_trampoline *tr = prog->aux->trampoline;
>>> + void *old_image = tr->image + ((tr->selector + 1) & 1) * PAGE_SIZE/2;
>>> + void *new_image = tr->image + (tr->selector & 1) * PAGE_SIZE/2;
>>> + if (err)
>>> + goto out;
>>> + tr->selector++;
>>
>> Shall we do selector-- for unlink?
>
> It's a bit flip. I think it would be more confusing with --
Right.. Maybe should use int instead of u64 for selector?
