[PATCH v3 6/9] kvm: arm/arm64: Add host pmu to support VM introspection
mark.rutland at arm.com
Wed Jan 18 10:05:46 PST 2017
On Wed, Jan 18, 2017 at 04:17:18PM +0000, Punit Agrawal wrote:
> Mark Rutland <mark.rutland at arm.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
> 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
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
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).
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