Re: [PATCH] unalias rework

[Marcelo Tosatti <mtosatti@redhat.com>]

Hi Izik,

On Thu, Sep 04, 2008 at 05:13:20PM +0300, izik eidus wrote:
>
> +		struct kvm_memory_slot *alias_slot = &kvm->memslots[i];
> +
> +		if (alias_slot->base_gfn == slot->base_gfn)
> +			return 1;
> +	}
> +	return 0;
> +}
> +
> +static void update_alias_slots(struct kvm *kvm, struct kvm_memory_slot *free)
> +{
> +	int i;
> +
> +	if (is_aliased_slot(kvm, free))
> +		return;
> +
> +	for (i = KVM_MEMORY_SLOTS; i < KVM_MEMORY_SLOTS + KVM_ALIAS_SLOTS;
> +	     ++i) {
> +		struct kvm_memory_slot *alias_memslot = &kvm->memslots[i];
> +		unsigned long size = free->npages << PAGE_SHIFT;
> +
> +		if (alias_memslot->userspace_addr >= free->userspace_addr &&
> +		    alias_memslot->userspace_addr < free->userspace_addr +
> +		    size) {
> +			alias_memslot->flags = free->flags;
> +			if (free->dirty_bitmap) {
> +				unsigned long offset =
> +						alias_memslot->userspace_addr -
> +						free->userspace_addr;
> +				unsigned dirty_offset;
> +				unsigned long bitmap_addr;
> +
> +				offset = offset >> PAGE_SHIFT;
> +				dirty_offset = ALIGN(offset, BITS_PER_LONG) / 8;
> +				bitmap_addr = (unsigned long) free->dirty_bitmap;
> +				bitmap_addr += dirty_offset;
> +				alias_memslot->dirty_bitmap = (unsigned long *) bitmap_addr;
> +			} else
> +				alias_memslot->dirty_bitmap = NULL;
> +		}
> +	}
> +}
> +
>  /*
>   * Free any memory in @free but not in @dont.
>   */
> -static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
> +static void kvm_free_physmem_slot(struct kvm *kvm,
> +				  struct kvm_memory_slot *free,
>  				  struct kvm_memory_slot *dont)
>  {
>  	if (!dont || free->rmap != dont->rmap)
> @@ -385,10 +433,16 @@ static void kvm_free_physmem_slot(struct kvm_memory_slot *free,
>  	if (!dont || free->lpage_info != dont->lpage_info)
>  		vfree(free->lpage_info);
>  
> -	free->npages = 0;
>  	free->dirty_bitmap = NULL;
>  	free->rmap = NULL;
>  	free->lpage_info = NULL;
> +
> +#ifdef CONFIG_X86
> +	update_alias_slots(kvm, free);
> +	if (dont)
> +		update_alias_slots(kvm, dont);
> +#endif
> +	free->npages = 0;

Why is this needed? I don't understand when would you free a memslot
without freeing any aliases that map it first?