KVM: x86/pmu: Snapshot and clear reprogramming bitmap before reprogramming
Refactor the handling of the reprogramming bitmap to snapshot and clear to-be-processed bits before doing the reprogramming, and then explicitly set bits for PMCs that need to be reprogrammed (again). This will allow adding a macro to iterate over all valid PMCs without having to add special handling for the reprogramming bit, which (a) can have bits set for non-existent PMCs and (b) needs to clear such bits to avoid wasting cycles in perpetuity. Note, the existing behavior of clearing bits after reprogramming does NOT have a race with kvm_vm_ioctl_set_pmu_event_filter(). Setting a new PMU filter synchronizes SRCU _before_ setting the bitmap, i.e. guarantees that the vCPU isn't in the middle of reprogramming with a stale filter prior to setting the bitmap. Link: https://lore.kernel.org/r/20231110022857.1273836-5-seanjc@google.com Signed-off-by:Sean Christopherson <seanjc@google.com>
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