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* [PATCH bpf-next v2] bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON
@ 2018-04-27 10:02 Leo Yan
  2018-04-27 10:10 ` Daniel Borkmann
  0 siblings, 1 reply; 2+ messages in thread
From: Leo Yan @ 2018-04-27 10:02 UTC (permalink / raw)
  To: Alexei Starovoitov, Daniel Borkmann, David S. Miller,
	Jonathan Corbet, netdev, linux-kernel, linux-doc
  Cc: Leo Yan

When CONFIG_BPF_JIT_ALWAYS_ON is enabled, kernel has limitation for
bpf_jit_enable, so it has fixed value 1 and we cannot set it to 2
for JIT opcode dumping; this patch is to update the doc for it.

Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
---
 Documentation/networking/filter.txt | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Documentation/networking/filter.txt b/Documentation/networking/filter.txt
index fd55c7d..5032e12 100644
--- a/Documentation/networking/filter.txt
+++ b/Documentation/networking/filter.txt
@@ -483,6 +483,12 @@ Example output from dmesg:
 [ 3389.935851] JIT code: 00000030: 00 e8 28 94 ff e0 83 f8 01 75 07 b8 ff ff 00 00
 [ 3389.935852] JIT code: 00000040: eb 02 31 c0 c9 c3
 
+When CONFIG_BPF_JIT_ALWAYS_ON is enabled, bpf_jit_enable is permanently set to 1 and
+setting any other value than that will return in failure. This is even the case for
+setting bpf_jit_enable to 2, since dumping the final JIT image into the kernel log
+is discouraged and introspection through bpftool (under tools/bpf/bpftool/) is the
+generally recommended approach instead.
+
 In the kernel source tree under tools/bpf/, there's bpf_jit_disasm for
 generating disassembly out of the kernel log's hexdump:
 
-- 
1.9.1

^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH bpf-next v2] bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON
  2018-04-27 10:02 [PATCH bpf-next v2] bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON Leo Yan
@ 2018-04-27 10:10 ` Daniel Borkmann
  0 siblings, 0 replies; 2+ messages in thread
From: Daniel Borkmann @ 2018-04-27 10:10 UTC (permalink / raw)
  To: Leo Yan, Alexei Starovoitov, David S. Miller, Jonathan Corbet,
	netdev, linux-kernel, linux-doc

On 04/27/2018 12:02 PM, Leo Yan wrote:
> When CONFIG_BPF_JIT_ALWAYS_ON is enabled, kernel has limitation for
> bpf_jit_enable, so it has fixed value 1 and we cannot set it to 2
> for JIT opcode dumping; this patch is to update the doc for it.
> 
> Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
> Signed-off-by: Leo Yan <leo.yan@linaro.org>

Applied to bpf-next, thanks Leo!

^ permalink raw reply	[flat|nested] 2+ messages in thread

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2018-04-27 10:02 [PATCH bpf-next v2] bpf, doc: Update bpf_jit_enable limitation for CONFIG_BPF_JIT_ALWAYS_ON Leo Yan
2018-04-27 10:10 ` Daniel Borkmann

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