KVM: x86: Treat KVM's virtual PMU as disabled for TDX VMs

Introduce a "protected PMU" concept, and use it to disable KVM's virtual
PMU for TDX VMs, as the PMU state for TDX VMs is virtualized by the TDX
Module[1], i.e. _can't_ emulated/virtualized by KVM, and KVM doesn't yet
support enabling/exposing PMU functionality for/to TDX VMs.  For now,
simply treat the PMU as disabled, as it's not clear what all needs to be
changed, e.g. KVM needs to do at least:

 1) Configure TD_PARAMS to allow guests to use performance monitoring.
 2) Restrict the TD to a subset of the PEBS counters if supported.
 3) Limit the TD to setup a certain perfmon events using basic/enhanced
    event filtering.

Explicitly disallow enabling the PMU via KVM_CAP_PMU_CAPABILITY for VMs
with a protected PMU to prevent userspace from circumventing KVM's
protections.

Link: https://cdrdv2.intel.com/v1/dl/getContent/733575 Section 15.2[1]
Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vishal Annapurve <vannapurve@google.com>
Link: https://patch.msgid.link/20260522151534.652522-1-vannapurve@google.com
[sean: massage shortlog and changelog]
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions