lkml.org 
[lkml]   [2020]   [Feb]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [RFC patch 09/19] bpf: Use BPF_PROG_RUN_PIN_ON_CPU() at simple call sites.
Date
Vinicius Costa Gomes <vinicius.gomes@intel.com> writes:

Cc+: seccomp folks

> Thomas Gleixner <tglx@linutronix.de> writes:
>
>> From: David Miller <davem@davemloft.net>

Leaving content for reference

>> All of these cases are strictly of the form:
>>
>> preempt_disable();
>> BPF_PROG_RUN(...);
>> preempt_enable();
>>
>> Replace this with BPF_PROG_RUN_PIN_ON_CPU() which wraps BPF_PROG_RUN()
>> with:
>>
>> migrate_disable();
>> BPF_PROG_RUN(...);
>> migrate_enable();
>>
>> On non RT enabled kernels this maps to preempt_disable/enable() and on RT
>> enabled kernels this solely prevents migration, which is sufficient as
>> there is no requirement to prevent reentrancy to any BPF program from a
>> preempting task. The only requirement is that the program stays on the same
>> CPU.
>>
>> Therefore, this is a trivially correct transformation.
>>
>> [ tglx: Converted to BPF_PROG_RUN_PIN_ON_CPU() ]
>>
>> Signed-off-by: David S. Miller <davem@davemloft.net>
>> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
>>
>> ---
>> include/linux/filter.h | 4 +---
>> kernel/seccomp.c | 4 +---
>> net/core/flow_dissector.c | 4 +---
>> net/core/skmsg.c | 8 ++------
>> net/kcm/kcmsock.c | 4 +---
>> 5 files changed, 6 insertions(+), 18 deletions(-)
>>
>> --- a/include/linux/filter.h
>> +++ b/include/linux/filter.h
>> @@ -713,9 +713,7 @@ static inline u32 bpf_prog_run_clear_cb(
>> if (unlikely(prog->cb_access))
>> memset(cb_data, 0, BPF_SKB_CB_LEN);
>>
>> - preempt_disable();
>> - res = BPF_PROG_RUN(prog, skb);
>> - preempt_enable();
>> + res = BPF_PROG_RUN_PIN_ON_CPU(prog, skb);
>> return res;
>> }
>>
>> --- a/kernel/seccomp.c
>> +++ b/kernel/seccomp.c
>> @@ -268,16 +268,14 @@ static u32 seccomp_run_filters(const str
>> * All filters in the list are evaluated and the lowest BPF return
>> * value always takes priority (ignoring the DATA).
>> */
>> - preempt_disable();
>> for (; f; f = f->prev) {
>> - u32 cur_ret = BPF_PROG_RUN(f->prog, sd);
>> + u32 cur_ret = BPF_PROG_RUN_PIN_ON_CPU(f->prog, sd);
>>
>
> More a question really, isn't the behavior changing here? i.e. shouldn't
> migrate_disable()/migrate_enable() be moved to outside the loop? Or is
> running seccomp filters on different cpus not a problem?

In my understanding this is a list of filters and they are independent
of each other.

Kees, Will. Andy?

Thanks,

tglx

\
 
 \ /
  Last update: 2020-02-19 10:02    [W:0.092 / U:0.240 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site