linux-kernel - Re: [PATCH 4/4] kvm: Implement PEBS virtualization

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Date:	Thu, 19 Jun 2014 16:42:43 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Marcelo Tosatti <mtosatti@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>
CC:	Andi Kleen <andi@...stfloor.org>, peterz@...radead.org,
	gleb@...nel.org, eranian@...gle.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] kvm: Implement PEBS virtualization

Il 10/06/2014 23:06, Marcelo Tosatti ha scritto:
> > BTW how about general PMU migration? As far as I can tell there
> > is no code to save/restore the state for that currently, right?
>
> Paolo wrote support for it, recently. Paolo?

Yes, on the KVM side all that is needed is to special case MSR reads and 
writes that have side effects, for example:

         case MSR_CORE_PERF_GLOBAL_STATUS:
                 if (msr_info->host_initiated) {
                         pmu->global_status = data;
                         return 0;
                 }
                 break; /* RO MSR */
         case MSR_CORE_PERF_GLOBAL_OVF_CTRL:
                 if (!(data & (pmu->global_ctrl_mask & ~(3ull<<62)))) {
                         if (!msr_info->host_initiated)
                                 pmu->global_status &= ~data;
                         pmu->global_ovf_ctrl = data;
                         return 0;
                 }
                 break;

Right now this is only needed for writes.

Userspace then can read/write these MSRs, and add them to the migration 
stream.  QEMU has code for that.

Paolo
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