linux-kernel - Re: [PATCH] perf/x86/intel: Drop kernel samples even though :u is specified

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Message-ID: <94a086e2-af12-49e9-f9c7-5b4b1b83ddfb@linux.intel.com>
Date:   Mon, 22 May 2017 20:30:54 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Mark Rutland <mark.rutland@....com>
Cc:     acme@...nel.org, jolsa@...nel.org, mingo@...hat.com,
        alexander.shishkin@...ux.intel.com, Linux-kernel@...r.kernel.org,
        ak@...ux.intel.com, kan.liang@...el.com, yao.jin@...el.com,
        Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] perf/x86/intel: Drop kernel samples even though :u is
 specified



On 5/22/2017 5:26 PM, Peter Zijlstra wrote:
> On Mon, May 22, 2017 at 09:45:30AM +0100, Mark Rutland wrote:
>> On Mon, May 22, 2017 at 10:12:22AM +0800, Jin, Yao wrote:
>>> But the code is being ugly and hard to maintain. And frankly I don't
>>> know kernel address space for all arch.
>>>
>>> Any idea? Could we just do at x86 side this time?
>> Can we not check user_mode(regs) for all architectures?
>>
>> !user_mode(regs) implies a kernel sample.
> Yes, that should work at that point. We specifically already rely on
> user_mode() in the generic code.
>
> On x86 we specifically set regs->cs to match regs->ip (in cases where
> this isn't necessarily so) before calling into the generic code to make
> this work.
>
Got it.
Thanks Mark, thanks Peter!