Re: [PATCH RFC v2 00/17] KVM: x86/pmu: Add support to enable Guest PEBS via DS

[Peter Zijlstra]

On Mon, Nov 09, 2020 at 10:12:37AM +0800, Like Xu wrote:
> The Precise Event Based Sampling(PEBS) supported on Intel Ice Lake server
> platforms can provide an architectural state of the instruction executed
> after the instruction that caused the event. This patch set enables the
> the PEBS via DS feature for KVM (also non) Linux guest on the Ice Lake.
> The Linux guest can use PEBS feature like native:
> 
>   # perf record -e instructions:ppp ./br_instr a
>   # perf record -c 100000 -e instructions:pp ./br_instr a
> 
> If the counter_freezing is not enabled on the host, the guest PEBS will
> be disabled on purpose when host is using PEBS facility. By default,
> KVM disables the co-existence of guest PEBS and host PEBS.

Uuhh, what?!? counter_freezing should never be enabled, its broken. Let
me go delete all that code.