linux-kernel - Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples

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Date:   Tue, 11 Aug 2020 16:31:10 +0800
From:   "Jin, Yao" <yao.jin@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     mingo@...hat.com, oleg@...hat.com, acme@...nel.org,
        jolsa@...nel.org, Linux-kernel@...r.kernel.org, ak@...ux.intel.com,
        kan.liang@...el.com, yao.jin@...el.com,
        alexander.shishkin@...ux.intel.com, mark.rutland@....com
Subject: Re: [PATCH v1 2/2] perf/core: Fake regs for leaked kernel samples

Hi Peter,

On 8/11/2020 3:59 PM, Peter Zijlstra wrote:
> On Tue, Aug 11, 2020 at 03:50:43PM +0800, Jin, Yao wrote:
>> Could I post v2 which basically refers to your patch but removes some
>> conditions since I see some issues in test if we use these conditions.
>>
>>   1. Remove '!event->attr.exclude_hv || !event->attr.exclude_host ||
>>      !event->attr.exclude_guest' at the entry of sanitize_sample_regs().
>>
>>   2. Remove '!attr.exclude_hv || !attr.exclude_host || !attr.exclude_guest'
>>      at the perf_event_open syscall entry.
> 
> exclude_host, maybe -- due to the dodgy semantics of it, but the others
> should definitely be there.
> 

exclude_guest and exclude_hv are tricky too.

If we do 'perf record -e cycles:u' in both host and guest, we can see:

event->attr.exclude_guest = 0

thus sanitize_sample_regs() returns regs directly even if exclude_kernel = 1.

And in guest, exclude_hv = 0, it's out of my expectation too.

Thanks
Jin Yao