LoongArch: KVM: Discard dirty page tracking on readonly memslot

For readonly memslot such as UEFI BIOS or UEFI var space, guest cannot
write this memory space directly. So it is not necessary to track dirty
pages for readonly memslot. Here we make such optimization in function
kvm_arch_commit_memory_region().
Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/kvm/mmu.c

@@ -444,6 +444,17 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 				   enum kvm_mr_change change)
 {
 	int needs_flush;
+	u32 old_flags = old ? old->flags : 0;
+	u32 new_flags = new ? new->flags : 0;
+	bool log_dirty_pages = new_flags & KVM_MEM_LOG_DIRTY_PAGES;
+
+	/* Only track memslot flags changed */
+	if (change != KVM_MR_FLAGS_ONLY)
+		return;
+
+	/* Discard dirty page tracking on readonly memslot */
+	if ((old_flags & new_flags) & KVM_MEM_READONLY)
+		return;
 
 	/*
 	 * If dirty page logging is enabled, write protect all pages in the slot
@@ -454,9 +465,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	 * 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)) {
+	if (!(old_flags & KVM_MEM_LOG_DIRTY_PAGES) && log_dirty_pages) {
 		spin_lock(&kvm->mmu_lock);
 		/* Write protect GPA page table entries */
 		needs_flush = kvm_mkclean_gpa_pt(kvm, new->base_gfn,