Re: [PATCH 1/1] bpf: avoid unnecessary IPI in bpf_flush_icache

On 6/3/21 1:26 AM, Will Deacon wrote:

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On Wed, Jun 02, 2021 at 07:26:03PM +0800, Xu, Yanfei wrote:

quoted

On 6/2/21 1:41 AM, Will Deacon wrote:

quoted

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On Tue, Jun 01, 2021 at 07:20:04PM +0200, Daniel Borkmann wrote:

quoted

On 6/1/21 5:06 PM, Yanfei Xu wrote:

quoted

It's no need to trigger IPI for keeping pipeline fresh in bpf case.

This needs a more concrete explanation/analysis on "why it is safe" to do so
rather than just saying that it is not needed.

Agreed. You need to show how the executing thread ends up going through a
context synchronizing operation before jumping to the generated code if
the IPI here is removed.

This patch came out with I looked through ftrace codes. Ftrace modify
the text code and don't send IPI in aarch64_insn_patch_text_nosync(). I
mistakenly thought the bpf is same with ftrace.

But now I'm still not sure why the ftrace don't need the IPI to go
through context synchronizing, maybe the worst situation is omit a
tracing event?

I think ftrace handles this itself via ftrace_sync_ipi, no?

Ah, Yes! I missed this...

Anyway, thanks for your reminding and very sorry for my noise.

Regards,
Yanfei

Will