Re: [PATCH v7 2/9] target/i386: disable PERFCORE when "-pmu" is configured

[Zhao Liu <zhao1.liu@intel.com>]

> Please let me know whether you would like to include Patch 2 on
> "amd_perfmon_always_on" as part of the "compat_prop" patch, or if you'd prefer
> that I re-create Patch 2 with your Suggested-by.
> 
> Either option works for me.

I took some time to revisit the dependency issues with PDCM again, and I
do think the approach mentioned in previous reply should work.

Ok, let me pick your patch 1 & 2. I will rebase these on the CET series
(since I've also modified the dependency for Arch LBR). The entire
dependency fix series may take some time and may need to wait for
several weeks.

However, at least it's decoupled from the rest. :)

At the same time, I'll help go through the remaining patches 3-9 again,
as it's been quite a while since I last reviewed them.

> It seems the Patches 3 - 9 are not impacted by this Live Migration issue.
> Perhaps they may be accepted (or as well as Patch 2 "amd_perfmon_always_on")
> without "compat_prop" patch? They are independent with each other.

Yes, I think so.

> Another concern is Patch 3. Something unexpected may occur when live migrating
> from a KVM host without KVM_PMU_CAP_DISABLE to one that has it enabled. The
> migration will succeed, but the perceived perf/vPMU support could change.
> Can we assume it is the user's responsibility to ensure compatibility between
> KVM hosts when "-pmu" is specified?

Yes, I think so, too. I understand that QEMU needs to ensure vmstate
migration compatibility.

Thanks,
Zhao