On Mon, Jul 24, 2023, Xu Yilun wrote:

On 2023-07-18 at 16:44:51 -0700, Sean Christopherson wrote:

quoted

@@ -1346,6 +1350,9 @@ static void kvm_destroy_vm(struct kvm *kvm)
 		kvm_free_memslots(kvm, &kvm->__memslots[i][0]);
 		kvm_free_memslots(kvm, &kvm->__memslots[i][1]);
 	}
+#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
+	xa_destroy(&kvm->mem_attr_array);
+#endif

Is it better to make the destruction in reverse order from the creation?

Yeah.  It _shoudn't_ matter, but there's no reason not keep things tidy and
consistent.

To put xa_destroy(&kvm->mem_attr_array) after cleanup_srcu_struct(&kvm->srcu),
or put xa_init(&kvm->mem_attr_array) after init_srcu_struct(&kvm->irq_srcu).

The former, because init_srcu_struct() can fail (allocates memory), whereas
xa_init() is a "pure" initialization routine.

quoted

 	cleanup_srcu_struct(&kvm->irq_srcu);
 	cleanup_srcu_struct(&kvm->srcu);
 	kvm_arch_free_vm(kvm);

@@ -2346,6 +2353,145 @@ static int kvm_vm_ioctl_clear_dirty_log(struct kvm *kvm,
 }
 #endif /* CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT */

[...]

quoted

+static int kvm_vm_ioctl_set_mem_attributes(struct kvm *kvm,
+					   struct kvm_memory_attributes *attrs)
+{
+	gfn_t start, end;
+
+	/* flags is currently not used. */
+	if (attrs->flags)
+		return -EINVAL;
+	if (attrs->attributes & ~kvm_supported_mem_attributes(kvm))
+		return -EINVAL;
+	if (attrs->size == 0 || attrs->address + attrs->size < attrs->address)
+		return -EINVAL;
+	if (!PAGE_ALIGNED(attrs->address) || !PAGE_ALIGNED(attrs->size))
+		return -EINVAL;
+
+	start = attrs->address >> PAGE_SHIFT;
+	end = (attrs->address + attrs->size - 1 + PAGE_SIZE) >> PAGE_SHIFT;

As the attrs->address/size are both garanteed to be non-zero, non-wrap
and page aligned in prevous check. Is it OK to simplify the calculation,
like:

  end = (attrs->address + attrs->size) >> PAGE_SHIFT;

Yes, that should work.

Chao, am I missing something?  Or did we just end up with unnecessarly convoluted
code as things evolved?

quoted

+
+	if (WARN_ON_ONCE(start == end))
+		return -EINVAL;

Also, is this check possible to be hit? Maybe remove it?

It should be impossible to, hence the WARN.  I added the check for two reasons:
(1) to help document that end is exclusive, and (2) to guard against future bugs.