From: Alexei Starovoitov <ast@fb.com>
To: Rick Edgecombe <rick.p.edgecombe@intel.com>,
"daniel@iogearbox.net" <daniel@iogearbox.net>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
"ard.biesheuvel@linaro.org" <ard.biesheuvel@linaro.org>,
"dave.hansen@intel.com" <dave.hansen@intel.com>,
"kristen@linux.intel.com" <kristen@linux.intel.com>
Subject: Re: [RFC PATCH 0/4] Initial support for allocating BPF JITs in vmalloc for x86
Date: Wed, 6 Feb 2019 00:35:50 +0000 [thread overview]
Message-ID: <84060613-48b1-fa62-e784-104faa7fc665@fb.com> (raw)
In-Reply-To: <20190205225103.28296-1-rick.p.edgecombe@intel.com>
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 ?
Nack.
next prev parent reply other threads:[~2019-02-06 0:36 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-05 22:50 [RFC PATCH 0/4] Initial support for allocating BPF JITs in vmalloc for x86 Rick Edgecombe
2019-02-05 22:51 ` [RFC PATCH 1/4] bpf, x64: Implement BPF call retpoline Rick Edgecombe
2019-02-05 22:51 ` [RFC PATCH 2/4] bpf, x64: Increase distance for bpf calls Rick Edgecombe
2019-02-05 22:51 ` [RFC PATCH 3/4] bpf: Charge bpf jit limit in bpf_jit_alloc_exec Rick Edgecombe
2019-02-05 22:51 ` [RFC PATCH 4/4] bpf, x64: Enable unprivlidged jit in vmalloc Rick Edgecombe
2019-02-06 0:35 ` Alexei Starovoitov [this message]
2019-02-06 1:11 ` [RFC PATCH 0/4] Initial support for allocating BPF JITs in vmalloc for x86 Edgecombe, Rick P
2019-02-06 1:40 ` Alexei Starovoitov
2019-02-06 15:38 ` Daniel Borkmann
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