Re: [PATCH RESEND] perf/x86/core: Completely disable guest PEBS via guest's global_ctrl

[Peter Zijlstra]

On Wed, Aug 31, 2022 at 11:35:24AM +0800, Like Xu wrote:
> From: Like Xu <likexu@xxxxxxxxxxx>
> 
> When a guest PEBS counter is cross-mapped by a host counter, software
> will remove the corresponding bit in the arr[global_ctrl].guest and
> expect hardware to perform a change of state "from enable to disable"
> via the msr_slot[] switch during the vmx transaction.
> 
> The real world is that if user adjust the counter overflow value small
> enough, it still opens a tiny race window for the previously PEBS-enabled
> counter to write cross-mapped PEBS records into the guest's PEBS buffer,
> when arr[global_ctrl].guest has been prioritised (switch_msr_special stuff)
> to switch into the enabled state, while the arr[pebs_enable].guest has not.
> 
> Close this window by clearing invalid bits in the arr[global_ctrl].guest.
> 
> Cc: linux-perf-users@xxxxxxxxxxxxxxx
> Cc: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Fixes: 854250329c02 ("KVM: x86/pmu: Disable guest PEBS temporarily in two rare situations")
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>
> ---

Thanks!