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Date:   Wed, 6 Feb 2019 00:35:50 +0000
From:   Alexei Starovoitov <>
To:     Rick Edgecombe <>,
        "" <>
CC:     "" <>,
        "" <>,
        "" <>,
        "" <>
Subject: Re: [RFC PATCH 0/4] Initial support for allocating BPF JITs in
 vmalloc for x86

On 2/5/19 2:50 PM, Rick Edgecombe wrote:
> This introduces a new capability for BPF program JIT's to be located in vmalloc
> space on x86_64. This can serve as a backup area for CONFIG_BPF_JIT_ALWAYS_ON in
> case an unprivileged app uses all of the module space allowed by bpf_jit_limit.
> In order to allow for calls from the increased distance of vmalloc from
> kernel/module space, relative calls are emitted as full indirect calls if the
> maximum relative call distance is exceeded. So the resulting performance of call
> BPF instructions in this case is similar to the BPF interpreter.

If I read this correctly the patches introduce retpoline overhead
to direct function call because JITed progs are more than 32-bit apart
and they're far away only because of dubious security concern ?

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