Re: [PATCH] x86/bpf: make arch_bpf_trampoline_size allocate from EXECMEM_MODULE_DATA

[Daniel Borkmann <daniel@iogearbox.net>]

On 8/19/26 8:42 AM, Mike Rapoport wrote:
> On Tue, Aug 18, 2026 at 02:07:23PM +0000, bot+bpf-ci@kernel.org wrote:
>>>      x86/bpf: make arch_bpf_trampoline_size allocate from EXECMEM_MODULE_DATA
>>>
>>>      Jiri Olsa reports slowdown of tracing_multi benchmark that allocates huge
>>>      number of trampolines [1].
>>>
>>>      The slowdown caused by extra protection changes in execmem_alloc_rw() and
>>>      execmem_free().
>>>
>>>      With ROX caches enabled, all execmem allocations except EXECMEM_MODULE_DATA
>>>      are ROX after the allocation. execmem_alloc_rw() temporarily sets them to
>>>      W+NX and execmem_free() resets them back to ROX.
>>>
>>>      The only user of bpf_jit_alloc_exec_rw() is x86::arch_bpf_trampoline_size()
>>>      that only needs a temporary writable buffer in the modules address space.
>>>
>>>      On x86 executable memory and module data are constrained to the same
>>>      address range, so x86::arch_bpf_trampoline_size() can directly use
>>>      execmem_alloc(EXECMEM_MODULE_DATA)
>>>
>>>      Replace the call to bpf_jit_alloc_exec_rw() with a call to
>>>      execmem_alloc(EXECMEM_MODULE_DATA) in x86::arch_bpf_trampoline_size() and
>>>      drop bpf_jit_alloc_exec_rw() helper.
>>>
>>>      Reported-by: Jiri Olsa <olsajiri@gmail.com>
>>>      Link: https://lore.kernel.org/all/an8r7EODLIL-bZM3@krava
>>>      Fixes: f0334294a428 ("bpf, x86: make sure allocation in arch_bpf_trampoline_size() is writable")
>>               ^^^^^^^^^^^^
>>
>> The Fixes tag references commit f0334294a428, which does not exist in
>> this repository. Should this be:
>>
>>    Fixes: 5bf02dbf39fa ("bpf, x86: Make sure allocation in arch_bpf_trampoline_size() is writable")
> 
> Argh, checked the log on a wrong branch.
> 
> Can you folks fix it up when applying or you'd need v3?

Yeap, we'll do, np.

>> That commit introduced bpf_jit_alloc_exec_rw() and the performance issue
>> being addressed here.
>