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bpf.2: Kernel 4.15 added CONFIG_BPF_JIT_ALWAYS_ON 

This causes the JIT compiler to be always on and
forces bpf_jit_enable to 1.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2018-03-05 15:36:26 +01:00
parent 036b0619f7
commit 5a29959a67
1 changed files with 13 additions and 1 deletions
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14
man2/bpf.2
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@ -1152,7 +1152,8 @@ files in the kernel source tree.
.PP
The kernel contains a just-in-time (JIT) compiler that translates
eBPF bytecode into native machine code for better performance.
The JIT compiler is disabled by default,
In kernels before Linux 4.15,
the JIT compiler is disabled by default,
but its operation can be controlled by writing one of the
following integer strings to the file
.IR /proc/sys/net/core/bpf_jit_enable :
@ -1167,6 +1168,17 @@ These opcodes can then be disassembled using the program
.IR tools/net/bpf_jit_disasm.c
provided in the kernel source tree.
.PP
Since Linux 4.15,
.\" commit 290af86629b25ffd1ed6232c4e9107da031705cb
the kernel may configured with the
.B CONFIG_BPF_JIT_ALWAYS_ON
option.
In this case, the JIT compiler is always enabled, and the
.I bpf_jit_enable
is initialized to 1 and is immutable.
(This kernel configuration option was provided as a mitigation for
one of the Spectre attacks against the BPF interpreter.)
.PP
JIT compiler for eBPF is currently available for the x86-64, arm64,
and s390 architectures.
.SH SEE ALSO