KVM: nVMX: Mark vmcs12's APIC access page dirty when unmapping

KVM: nVMX: Mark vmcs12's APIC access page dirty when unmapping

Mark the APIC access page as dirty when unmapping it from KVM.  The fact
that the page _shouldn't_ be written doesn't guarantee the page _won't_ be
written.  And while the contents are likely irrelevant, the values _are_
visible to the guest, i.e. dropping writes would be visible to the guest
(though obviously highly unlikely to be problematic in practice).

Marking the map dirty will allow specifying the write vs. read-only when
*mapping* the memory, which in turn will allow creating read-only maps.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <20241010182427.1434605-33-seanjc@google.com>