Re: [PATCH][1/3] Move kvm_vcpu_iotcl_get_dirty_log to arch

[Carsten Otte <cotte-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>]

Zhang, Xiantao wrote:
> Move kvm_vcpu_ioctl_get_dirty_log to arch, and still keep the interface
> in common.

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index 45b18e1..3400265 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -419,19 +419,14 @@ int kvm_vm_ioctl_set_memory_region(struct kvm *kvm,
  	return kvm_set_memory_region(kvm, mem, user_alloc);
  }

-/*
- * Get (and clear) the dirty memory log for a memory slot.
- */
-static int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm,
-				      struct kvm_dirty_log *log)
+int kvm_get_dirty_log(struct kvm *kvm,
+			struct kvm_dirty_log *log, int *is_dirty)

Any reason to remove that comment? It looks helpful to me.


  {
  	struct kvm_memory_slot *memslot;
  	int r, i;
  	int n;
  	unsigned long any = 0;

-	mutex_lock(&kvm->lock);
-
  	r = -EINVAL;
  	if (log->slot >= KVM_MEMORY_SLOTS)
  		goto out;
@@ -450,17 +445,11 @@ static int kvm_vm_ioctl_get_dirty_log(struct kvm 
*kvm,
  	if (copy_to_user(log->dirty_bitmap, memslot->dirty_bitmap, n))
  		goto out;

-	/* If nothing is dirty, don't bother messing with page tables. */
-	if (any) {
-		kvm_mmu_slot_remove_write_access(kvm, log->slot);
-		kvm_flush_remote_tlbs(kvm);
-		memset(memslot->dirty_bitmap, 0, n);
-	}
+	if (any)
+		*is_dirty = 1;

  	r = 0;
-
  out:
-	mutex_unlock(&kvm->lock);
  	return r;
  }

This split won't work on s390. I think kvm_get_dirty_log should be 
arch dependent alltogether: we're not going to have a dirty bitmap on 
s390, we rather rely on our hardware support to update our storage 
keys accordingly without guest/host intervention required. We'd want 
to use that, and thus this implementation of kvm_get_dirty_log makes 
no sense for us. On the other hand, I'd really want to keep the ioctl 
common, so that guest migration code in userland can be common for all 
archs.

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