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

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Message-ID: <20230612100502.GE217089@leoy-huanghe.lan>
Date:   Mon, 12 Jun 2023 18:05:02 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Shuai Xue <xueshuai@...ux.alibaba.com>
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 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.

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.

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.

Thanks,
Leo