KVM: MIPS: Clean & flush on dirty page logging enable

When an existing memory region has dirty page logging enabled, make the
entire slot clean (read only) so that writes will immediately start
logging dirty pages (once the dirty bit is transferred from GPA to GVA
page tables in an upcoming patch).

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Radim Krčmář" <rkrcmar@redhat.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: linux-mips@linux-mips.org
Cc: kvm@vger.kernel.org

arch/mips/kvm/mips.c

@@ -197,9 +197,33 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				   const struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
+	int needs_flush;
+
 	kvm_debug("%s: kvm: %p slot: %d, GPA: %llx, size: %llx, QVA: %llx\n",
 		  __func__, kvm, mem->slot, mem->guest_phys_addr,
 		  mem->memory_size, mem->userspace_addr);
+
+	/*
+	 * If dirty page logging is enabled, write protect all pages in the slot
+	 * ready for dirty logging.
+	 *
+	 * There is no need to do this in any of the following cases:
+	 * CREATE:	No dirty mappings will already exist.
+	 * MOVE/DELETE:	The old mappings will already have been cleaned up by
+	 *		kvm_arch_flush_shadow_memslot()
+	 */
+	if (change == KVM_MR_FLAGS_ONLY &&
+	    (!(old->flags & KVM_MEM_LOG_DIRTY_PAGES) &&
+	     new->flags & KVM_MEM_LOG_DIRTY_PAGES)) {
+		spin_lock(&kvm->mmu_lock);
+		/* Write protect GPA page table entries */
+		needs_flush = kvm_mips_mkclean_gpa_pt(kvm, new->base_gfn,
+					new->base_gfn + new->npages - 1);
+		/* Let implementation do the rest */
+		if (needs_flush)
+			kvm_mips_callbacks->flush_shadow_memslot(kvm, new);
+		spin_unlock(&kvm->mmu_lock);
+	}
 }
 
 static inline void dump_handler(const char *symbol, void *start, void *end)