linux-kernel - Re: [PATCH 10/10] perf/doc: update design.txt for exclude

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87bm5sxqya.fsf@concordia.ellerman.id.au>
Date:   Tue, 11 Dec 2018 22:06:53 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Andrew Murray <andrew.murray@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        linux-alpha@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        "paulus\@samba.org" <paulus@...ba.org>
Subject: Re: [PATCH 10/10] perf/doc: update design.txt for exclude_{host|guest} flags

[ Reviving old thread. ]

Andrew Murray <andrew.murray@....com> writes:
> On Tue, Nov 20, 2018 at 10:31:36PM +1100, Michael Ellerman wrote:
>> Andrew Murray <andrew.murray@....com> writes:
>> 
>> > Update design.txt to reflect the presence of the exclude_host
>> > and exclude_guest perf flags.
>> >
>> > Signed-off-by: Andrew Murray <andrew.murray@....com>
>> > ---
>> >  tools/perf/design.txt | 4 ++++
>> >  1 file changed, 4 insertions(+)
>> >
>> > diff --git a/tools/perf/design.txt b/tools/perf/design.txt
>> > index a28dca2..7de7d83 100644
>> > --- a/tools/perf/design.txt
>> > +++ b/tools/perf/design.txt
>> > @@ -222,6 +222,10 @@ The 'exclude_user', 'exclude_kernel' and 'exclude_hv' bits provide a
>> >  way to request that counting of events be restricted to times when the
>> >  CPU is in user, kernel and/or hypervisor mode.
>> >  
>> > +Furthermore the 'exclude_host' and 'exclude_guest' bits provide a way
>> > +to request counting of events restricted to guest and host contexts when
>> > +using virtualisation.
>> 
>> How does exclude_host differ from exclude_hv ?
>
> I believe exclude_host / exclude_guest are intented to distinguish
> between host and guest in the hosted hypervisor context (KVM).

OK yeah, from the perf-list man page:

           u - user-space counting
           k - kernel counting
           h - hypervisor counting
           I - non idle counting
           G - guest counting (in KVM guests)
           H - host counting (not in KVM guests)

> Whereas exclude_hv allows to distinguish between guest and
> hypervisor in the bare-metal type hypervisors.

Except that's exactly not how we use them on powerpc :)

We use exclude_hv to exclude "the hypervisor", regardless of whether
it's KVM or PowerVM (which is a bare-metal hypervisor).

We don't use exclude_host / exclude_guest at all, which I guess is a
bug, except I didn't know they existed until this thread.

eg, in a KVM guest:

  $ perf record -e cycles:G /bin/bash -c "for i in {0..100000}; do :;done"
  $ perf report -D | grep -Fc "dso: [hypervisor]"
  16


> In the case of arm64 - if VHE extensions are present then the host
> kernel will run at a higher privilege to the guest kernel, in which
> case there is no distinction between hypervisor and host so we ignore
> exclude_hv. But where VHE extensions are not present then the host
> kernel runs at the same privilege level as the guest and we use a
> higher privilege level to switch between them - in this case we can
> use exclude_hv to discount that hypervisor role of switching between
> guests.

I couldn't find any arm64 perf code using exclude_host/guest at all?

And I don't see any x86 code using exclude_hv.

But maybe that's OK, I just worry this is confusing for users.

cheers