From: Tamas K Lengyel <tamas.k.lengyel@gmail.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: "Kevin Tian" <kevin.tian@intel.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Julien Grall" <julien@xen.org>,
"Jun Nakajima" <jun.nakajima@intel.com>, "Wei Liu" <wl@xen.org>,
"Michał Leszczyński" <michal.leszczynski@cert.pl>,
"Ian Jackson" <ian.jackson@eu.citrix.com>,
"George Dunlap" <george.dunlap@citrix.com>,
"Jan Beulich" <jbeulich@suse.com>,
Xen-devel <xen-devel@lists.xenproject.org>,
"Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH v1 0/7] Implement support for external IPT monitoring
Date: Wed, 17 Jun 2020 13:31:49 -0600 [thread overview]
Message-ID: <CABfawhmJR6c4+sv5g_4STf3k2Vif-jmtOjJzLLqKWmh6gmt4_Q@mail.gmail.com> (raw)
In-Reply-To: <2df6eecb-df3b-7f6e-4185-99f4244ed9d1@citrix.com>
On Wed, Jun 17, 2020 at 11:23 AM Andrew Cooper
<andrew.cooper3@citrix.com> wrote:
>
> On 17/06/2020 17:27, Tamas K Lengyel wrote:
> >>>>>> What semantics do you want for the buffer becoming full? Given that
> >>>>>> debugging/tracing is the goal, I presume "pause vcpu on full" is the
> >>>>>> preferred behaviour, rather than drop packets on full?
> >>>>>>
> >>>>> Right now this is a ring-style buffer and when it would become full it would simply wrap and override the old data.
> >>>> How does the consumer spot that the data has wrapped? What happens if
> >>>> data starts getting logged, but noone is listening? What happens if the
> >>>> consumer exits/crashes/etc and stops listening as a consequence?
> >>>>
> >>>> It's fine to simply state what will happen, and possibly even "don't do
> >>>> that then", but the corner cases do at least need thinking about.
> >>> AFAIU the current use-case is predominantly to be used in conjunction
> >>> with VMI events where you want to be able to see the trace leading up
> >>> to a particular vmexit. So in the case when the buffer is wrapped
> >>> in-between events and data is lost that's not really of concern.
> >> That's all fine. I imagine the output here is voluminous, and needs
> >> help being cut down as much as possible.
> >>
> >> On a tangent, I presume you'd like to include VM-fork eventually, which
> >> ought to include copying the trace buffer on fork?
> > I would eventually like to use it to reconstruct the branch history so
> > we can update AFL's coverage map with that instead of having to do the
> > current breakpoint-singlestep dance. But for that I would only care
> > about the trace starting after the fork, so copying the parent's PT
> > buffer is not needed. We'll also probably only use PT if the branch
> > history is larger than what LBR can hold. I asked Michal to name the
> > hypercall interface "vmtrace" for this reason so we can add other
> > stuff like LBR later using the same interface (which I already
> > implemented in https://github.com/tklengyel/xen/commits/lbr).
>
> I was wondering when someone was going to want LBR data like this.
> Can't you borrow the LBR-stitching tricks from Linux's perf to recover
> the call trace even when its deeper than the LBR stack?
TBH I only spent like an hour putting it together so I haven't
investigated the topic too much. But thanks for the tip, first I heard
about this LBR-stitching trick ;)
>
> What about PEBS? ISTR there is a fairly complicated matrix of which
> features work in combination.
There is also BTS.. I would assume it would take some experimentation
to figure out what works and when and in what combination. Right now I
have no plans for doing that experimentation or adding support for
additional tracers.
>
>
> As for naming, we should definitely have something fairly generic.
> AFAICT, it would be applicable to ARM's CoreSight facilities as well.
IMHO XEN_DOMCTL_vmtrace would be a good name for controlling these features.
Tamas
next prev parent reply other threads:[~2020-06-17 19:32 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-16 15:16 [PATCH v1 0/7] Implement support for external IPT monitoring Michał Leszczyński
2020-06-16 15:19 ` [PATCH v1 1/7] x86/vmx: add Intel PT MSR definitions Michał Leszczyński
2020-06-18 13:31 ` Jan Beulich
2020-06-16 15:20 ` [PATCH v1 2/7] x86/vmx: add IPT cpu feature Michał Leszczyński
2020-06-16 16:30 ` Roger Pau Monné
2020-06-17 11:34 ` Jan Beulich
2020-06-16 15:21 ` [PATCH v1 3/7] x86/vmx: add ipt_state as part of vCPU state Michał Leszczyński
2020-06-16 16:33 ` Roger Pau Monné
2020-06-16 15:22 ` [PATCH v1 4/7] x86/vmx: add do_vmtrace_op Michał Leszczyński
2020-06-16 17:23 ` Roger Pau Monné
2020-06-17 19:13 ` Michał Leszczyński
2020-06-18 3:20 ` Tamas K Lengyel
2020-06-18 11:01 ` Michał Leszczyński
2020-06-18 11:55 ` Roger Pau Monné
2020-06-18 12:51 ` Jan Beulich
2020-06-18 13:09 ` Michał Leszczyński
2020-06-18 13:24 ` Jan Beulich
2020-06-18 13:40 ` Roger Pau Monné
2020-06-18 8:46 ` Roger Pau Monné
2020-06-18 15:25 ` Michał Leszczyński
2020-06-18 15:39 ` Jan Beulich
2020-06-18 15:47 ` Tamas K Lengyel
2020-06-18 15:49 ` Tamas K Lengyel
2020-06-16 15:22 ` [PATCH v1 5/7] tools/libxc: add xc_ptbuf_* functions Michał Leszczyński
2020-06-16 15:23 ` [PATCH v1 6/7] tools/proctrace: add proctrace tool Michał Leszczyński
2020-06-16 15:24 ` [PATCH v1 7/7] x86/vmx: switch IPT MSRs on vmentry/vmexit Michał Leszczyński
2020-06-16 17:38 ` Roger Pau Monné
2020-06-16 17:47 ` Michał Leszczyński
2020-06-17 9:09 ` Roger Pau Monné
2020-06-17 11:54 ` Michał Leszczyński
2020-06-17 12:51 ` Roger Pau Monné
2020-06-17 15:14 ` Andrew Cooper
2020-06-17 18:56 ` Michał Leszczyński
2020-06-18 8:52 ` Roger Pau Monné
2020-06-18 11:07 ` Michał Leszczyński
2020-06-18 11:49 ` Roger Pau Monné
2020-06-17 23:30 ` Kang, Luwei
2020-06-18 10:02 ` Andrew Cooper
2020-06-18 17:38 ` Andrew Cooper
2020-06-16 18:17 ` [PATCH v1 0/7] Implement support for external IPT monitoring Andrew Cooper
2020-06-16 18:47 ` Michał Leszczyński
2020-06-16 20:16 ` Andrew Cooper
2020-06-17 3:02 ` Tamas K Lengyel
2020-06-17 16:19 ` Andrew Cooper
2020-06-17 16:27 ` Tamas K Lengyel
2020-06-17 17:23 ` Andrew Cooper
2020-06-17 19:31 ` Tamas K Lengyel [this message]
2020-06-17 19:30 ` Michał Leszczyński
2020-06-17 20:20 ` Michał Leszczyński
2020-06-18 8:25 ` Roger Pau Monné
2020-06-18 14:59 ` Michał Leszczyński
2020-06-17 1:35 ` Tian, Kevin
2020-06-17 6:45 ` Kang, Luwei
2020-06-17 9:21 ` Roger Pau Monné
2020-06-17 12:37 ` Kang, Luwei
2020-06-17 12:53 ` Roger Pau Monné
2020-06-17 23:29 ` Kang, Luwei
2020-06-18 0:56 ` Michał Leszczyński
2020-06-18 7:00 ` Roger Pau Monné
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