linux-kernel - Re: [PATCH 1/2] perf/core: Bail out early if the request AUX area is out of bound

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Date:   Tue, 13 Jun 2023 11:00:11 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     alexander.shishkin@...ux.intel.com, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        jolsa@...nel.org, namhyung@...nel.org, irogers@...gle.com,
        adrian.hunter@...el.com, linux-perf-users@...r.kernel.org,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
        Baolin Wang <baolin.wang@...ux.alibaba.com>
Subject: Re: [PATCH 1/2] perf/core: Bail out early if the request AUX area is
 out of bound



On 2023/6/12 18:25, Leo Yan wrote:
> On Mon, Jun 12, 2023 at 06:05:02PM +0800, Leo Yan wrote:
>> On Mon, Jun 12, 2023 at 04:35:07PM +0800, Shuai Xue wrote:
>>
>> [...]
>>
>>>> Furthermore, I believe the AUX trace pages are only mapped for VMA
>>>> (continuous virtual address), the kernel will defer to map to physical
>>>> pages (which means it's not necessarily continuous physical pages)
>>>> when handling data abort caused by accessing the pages.
>>>
>>> I don't know why the rb->aux_pages is limit to allocated with continuous physical pages.
>>> so I just add a check to avoid oops and report a proper error code -EINVAL to
>>> user.
>>>
>>> I would like to use vmalloc() family to replace kmalloc() so that we could support
>>> allocate a more large AUX area if it is not necessarily continuous physical pages.
>>> Should we remove the restriction?
>>
>> As you said, we are now able to support a maximum AUX trace buffer
>> size of up to 2GiB, and AUX trace buffer is per CPU wise.
> 
> Ouch, I reviewed my notes and correct myself:
> 
> For per thread mode, perf tool only allocates one generic ring buffer
> and one AUX ring buffer for the whole session; for the system wide mode,
> perf allocates the generic ring buffer and the AUX ring buffer per CPU
> wise.
> 
>> Seems to me, 2GiB AUX buffer per CPU is big enough for most tracing
>> scenarios, right?  Except you can provide profiling scenario which
>> must use bigger buffer size.
> 
> But I think this question is still valid.
> 
>> Another factor is the allocation of buffers from kmalloc() offers better
>> performance compared to allocation from vmalloc(), this is also
>> important for perf core layer.

I see, I don't have such profiling scenario, let's leave the restriction untouched
and I will move the sanity check into rb_alloc_aux().

>>
>> Thanks,
>> Leo

Thank you.

Best Regards,
Shuai