KVM: PPC: Book3S HV: Flush guest mappings when turning dirty tracking on/off

This adds code to flush the partition-scoped page tables for a radix
guest when dirty tracking is turned on or off for a memslot.  Only the
guest real addresses covered by the memslot are flushed.  The reason
for this is to get rid of any 2M PTEs in the partition-scoped page
tables that correspond to host transparent huge pages, so that page
dirtiness is tracked at a system page (4k or 64k) granularity rather
than a 2M granularity.  The page tables are also flushed when turning
dirty tracking off so that the memslot's address space can be
repopulated with THPs if possible.

To do this, we add a new function kvmppc_radix_flush_memslot().  Since
this does what's needed for kvmppc_core_flush_memslot_hv() on a radix
guest, we now make kvmppc_core_flush_memslot_hv() call the new
kvmppc_radix_flush_memslot() rather than calling kvm_unmap_radix()
for each page in the memslot.  This has the effect of fixing a bug in
that kvmppc_core_flush_memslot_hv() was previously calling
kvm_unmap_radix() without holding the kvm->mmu_lock spinlock, which
is required to be held.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Reviewed-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>

arch/powerpc/include/asm/kvm_book3s.h

@@ -222,6 +222,8 @@ extern int kvm_test_age_radix(struct kvm *kvm, struct kvm_memory_slot *memslot,
 			unsigned long gfn);
 extern long kvmppc_hv_get_dirty_log_radix(struct kvm *kvm,
 			struct kvm_memory_slot *memslot, unsigned long *map);
+extern void kvmppc_radix_flush_memslot(struct kvm *kvm,
+			const struct kvm_memory_slot *memslot);
 extern int kvmhv_get_rmmu_info(struct kvm *kvm, struct kvm_ppc_rmmu_info *info);
 
 /* XXX remove this export when load_last_inst() is generic */