linux-kernel - Re: [PATCH v3 6/9] kvm: arm/arm64: Add host pmu to support VM introspection

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: <20170118180546.GN3231@leverpostej>
Date:   Wed, 18 Jan 2017 18:05:46 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Punit Agrawal <punit.agrawal@....com>
Cc:     kvm@...r.kernel.org, Marc Zyngier <marc.zyngier@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 6/9] kvm: arm/arm64: Add host pmu to support VM
 introspection

On Wed, Jan 18, 2017 at 04:17:18PM +0000, Punit Agrawal wrote:
> Mark Rutland <mark.rutland@....com> writes:
> 
> > On Wed, Jan 18, 2017 at 02:51:31PM +0000, Punit Agrawal wrote:
> >> I should've clarified in my reply that I wasn't looking to support the
> >> third instance from Mark's examples above - "monitor all vCPUs on a
> >> pCPU". I think it'll be quite expensive to figure out which threads from
> >> a given pool are vCPUs.
> >
> > I'm not sure I follow why you would need to do that?
> >
> > In that case, we'd open a CPU-bound perf event for the pCPU, which would
> > get installed in the CPU context immediately. It would be present for
> > all tasks.
> >
> > Given it's present for all tasks, we don't need to figure out which
> > happen to have vCPUs. The !vCPU tasks simply shouldn't trigger events.
> >
> > Am I missing something?
> 
> When enabling a CPU-bound event for pCPU, we'd have to enable trapping
> of TLB operations for the vCPUs running on pCPU. Have a look at Patch
> 7/9.
> 
> Also, we'd have to enable/disable trapping when tasks are migrated
> between pCPUs.

Ah, so we can't configure the trap and leave it active, since it'll
affect the host.

We could have a per-cpu flag, and a hook into vcpu_run, but that's also
gnarly.

I'll have a think.

> So far I've assumed that a VM pid is immutable. If that doesn't hold
> then we need to think of another mechanism to refer to a VM from
> userspace.

Even if we can't migrate the VM between processes (i.e. it's immutable),
it's still not unique within a process, so I'm fairly sure we need
another mechanism (even if we get away with the common case today).

Thanks,
Mark.