Re: [PATCH v4 08/16] KVM: x86/pmu: Add IA32_DS_AREA MSR emulation to manage guest DS buffer

[Peter Zijlstra]

On Mon, Mar 29, 2021 at 01:41:29PM +0800, Like Xu wrote:
> @@ -3869,10 +3876,12 @@ static struct perf_guest_switch_msr *intel_guest_get_msrs(int *nr, void *data)
>  
>  		if (arr[1].guest)
>  			arr[0].guest |= arr[1].guest;
> -		else
> +		else {
>  			arr[1].guest = arr[1].host;
> +			arr[2].guest = arr[2].host;
> +		}

What's all this gibberish?

The way I read that it says:

	if guest has PEBS_ENABLED
		guest GLOBAL_CTRL |= PEBS_ENABLED
	otherwise
		guest PEBS_ENABLED = host PEBS_ENABLED
		guest DS_AREA = host DS_AREA

which is just completely random garbage afaict. Why would you leak host
msrs into the guest? Why would you change guest GLOBAL_CTRL implicitly;
guest had better wrmsr that himself to control when stuff is enabled.

This just cannot be right.