KVM: nVMX: Do a bitwise-AND of regs_avail when switching active VMCS

KVM: nVMX: Do a bitwise-AND of regs_avail when switching active VMCS

When switching between vmcs01 and vmcs02, do a bitwise-AND of regs_avail
to effectively reset the mask for the new VMCS, purely to be consistent
with all other "full" writes of regs_avail.  In practice, a straight write
versus a bitwise-AND will yield the same result, as kvm_arch_vcpu_create()
marks *all* registers available (and dirty), and KVM never marks registers
unavailable unless they're lazily loaded.

This will allow adding wrapper APIs to set regs_{avail,dirty} without
having to add special handling for a nVMX use case that doesn't exist in
practice.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Message-ID: <20260409224236.2021562-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>