linux-kernel - Re: [PATCH 6/6] perf intel-pt: Add guest

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Message-ID: <df56f04b-cb25-5a47-ffef-b2e2ee0f6b74@intel.com>
Date:   Fri, 13 May 2022 18:14:49 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        Ian Rogers <irogers@...gle.com>, Leo Yan <leo.yan@...aro.org>,
        linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH 6/6] perf intel-pt: Add guest_code support

On 13/05/22 17:46, Andi Kleen wrote:
> Adrian Hunter <adrian.hunter@...el.com> writes:
> 
>> A common case for KVM test programs is that the guest object code can be
>> found in the hypervisor process (i.e. the test program running on the
>> host). To support that, a new option "--guest-code" has been added in
>> previous patches.
>>
>> In this patch, add support also to Intel PT.
>>
>> In particular, ensure guest_code thread is set up before attempting to
>> walk object code or synthesize samples.
> 
> Can you make it clear in the documentation what parts runs on the host
> and what parts on the guest? 

That is up to the test program.  All the host thread maps are
copied, so perf tools doesn't have to know.

> 
> I'm still not fully sure how it exactly finds the code on the host,
> how is the code transferred?

I don't know.  From a quick look at the code in
tools/testing/selftests/kvm/lib/kvm_util.c it seems to be using
KVM_SET_USER_MEMORY_REGION IOCTL.

> 
> Other than that more support for this use case is very useful.
> 
> -Andi