KVM: x86/pmu: Reprogram Host/Guest-Only counters on nested transitions

Reprogram PMU counters on nested transitions for the mediated PMU, to
re-evaluate Host-Only and Guest-Only bits and enable/disable the PMU
counters accordingly. For example, if Host-Only is set and Guest-Only is
cleared, a counter should be disabled when entering guest mode and
enabled when exiting guest mode.

According to the APM, when EFER.SVME is cleared, setting Host-Only or
Guest-Only disables the counter, so also trigger counter reprogramming
when EFER.SVME is toggled.

Counters setting any of Host-Only and Guest-Only bits are already being
tracked in pmc_has_mode_specific_enables, use the bitmap to reprogram
these counters.

Reprogram the counters synchronously on nested VMRUN/#VMEXIT and
EFER.SVME toggling. This is necessary as these instructions are counted
based on the new CPU state (after the instruction is retired in
hardware).  Hence, the PMU needs to be updated before instruction
emulation is completed and kvm_pmu_instruction_retired() is called.

Defer reprogramming the counters when force leaving guest mode through
svm_leave_nested() to avoid potentially reading stale state (e.g.
incorrect EFER). All flows force leaving nested are non-architectural,
so accuracy is irrelevant.

Refactor a helper out of kvm_pmu_request_reprogram_counters() that
accepts a boolean allowing synchronous vs deferred reprogramming, and
use that from SVM code to support both scenarios.

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260527234711.4175166-13-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>

0 files changed, 0 insertions, 0 deletions