Re: [PATCH v2 06/13] KVM: arm64: Add support for KVM_MEM_USERFAULT

[Sean Christopherson <seanjc@google.com>]

On Thu, Jan 09, 2025, James Houghton wrote:
> @@ -2073,6 +2080,23 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>  				   enum kvm_mr_change change)
>  {
>  	bool log_dirty_pages = new && new->flags & KVM_MEM_LOG_DIRTY_PAGES;
> +	u32 new_flags = new ? new->flags : 0;
> +	u32 changed_flags = (new_flags) ^ (old ? old->flags : 0);

This is a bit hard to read, and there's only one use of log_dirty_pages.  With
zapping handled in common KVM, just do:

@@ -2127,14 +2131,19 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
                                   const struct kvm_memory_slot *new,
                                   enum kvm_mr_change change)
 {
-       bool log_dirty_pages = new && new->flags & KVM_MEM_LOG_DIRTY_PAGES;
+       u32 old_flags = old ? old->flags : 0;
+       u32 new_flags = new ? new->flags : 0;
+
+       /* Nothing to do if not toggling dirty logging. */
+       if (!((old_flags ^ new_flags) & KVM_MEM_LOG_DIRTY_PAGES))
+               return;
 
        /*
         * At this point memslot has been committed and there is an
         * allocated dirty_bitmap[], dirty pages will be tracked while the
         * memory slot is write protected.
         */
-       if (log_dirty_pages) {
+       if (new_flags & KVM_MEM_LOG_DIRTY_PAGES) {
 
                if (change == KVM_MR_DELETE)
                        return;