Subject: Re: [PATCH 05/13] KVM: Refactor error handling for setting memory region

From: Janosch Frank <[email-masked]>
Date: Thu, 12 Sep 2019 13:36:48 +0200

On 9/11/19 8:50 PM, Sean Christopherson wrote:
> Replace a big pile o' gotos with returns to make it more obvious what
> error code is being returned, and to prepare for refactoring the
> functional, i.e. post-checks, portion of __kvm_set_memory_region().
> 
> Signed-off-by: Sean Christopherson <[email-masked]>

Definitely necessary
Reviewed-by: Janosch Frank <[email-masked]>

> ---
>  virt/kvm/kvm_main.c | 40 ++++++++++++++++++----------------------
>  1 file changed, 18 insertions(+), 22 deletions(-)
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index ea8f2f37096f..8306ce3345a6 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -929,34 +929,33 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  
>  	r = check_memory_region_flags(mem);
>  	if (r)
> -		goto out;
> +		return r;
>  
> -	r = -EINVAL;
>  	as_id = mem->slot >> 16;
>  	id = (u16)mem->slot;
>  
>  	/* General sanity checks */
>  	if (mem->memory_size & (PAGE_SIZE - 1))
> -		goto out;
> +		return -EINVAL;
>  	if (mem->guest_phys_addr & (PAGE_SIZE - 1))
> -		goto out;
> +		return -EINVAL;
>  	/* We can read the guest memory with __xxx_user() later on. */
>  	if ((id < KVM_USER_MEM_SLOTS) &&
>  	    ((mem->userspace_addr & (PAGE_SIZE - 1)) ||
>  	     !access_ok((void __user *)(unsigned long)mem->userspace_addr,
>  			mem->memory_size)))
> -		goto out;
> +		return -EINVAL;
>  	if (as_id >= KVM_ADDRESS_SPACE_NUM || id >= KVM_MEM_SLOTS_NUM)
> -		goto out;
> +		return -EINVAL;
>  	if (mem->guest_phys_addr + mem->memory_size < mem->guest_phys_addr)
> -		goto out;
> +		return -EINVAL;
>  
>  	slot = id_to_memslot(__kvm_memslots(kvm, as_id), id);
>  	base_gfn = mem->guest_phys_addr >> PAGE_SHIFT;
>  	npages = mem->memory_size >> PAGE_SHIFT;
>  
>  	if (npages > KVM_MEM_MAX_NR_PAGES)
> -		goto out;
> +		return -EINVAL;
>  
>  	new = old = *slot;
>  
> @@ -973,20 +972,18 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  			if ((new.userspace_addr != old.userspace_addr) ||
>  			    (npages != old.npages) ||
>  			    ((new.flags ^ old.flags) & KVM_MEM_READONLY))
> -				goto out;
> +				return -EINVAL;
>  
>  			if (base_gfn != old.base_gfn)
>  				change = KVM_MR_MOVE;
>  			else if (new.flags != old.flags)
>  				change = KVM_MR_FLAGS_ONLY;
> -			else { /* Nothing to change. */
> -				r = 0;
> -				goto out;
> -			}
> +			else /* Nothing to change. */
> +				return 0;
>  		}
>  	} else {
>  		if (!old.npages)
> -			goto out;
> +			return -EINVAL;
>  
>  		change = KVM_MR_DELETE;
>  		new.base_gfn = 0;
> @@ -995,29 +992,29 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  
>  	if ((change == KVM_MR_CREATE) || (change == KVM_MR_MOVE)) {
>  		/* Check for overlaps */
> -		r = -EEXIST;
>  		kvm_for_each_memslot(slot, __kvm_memslots(kvm, as_id)) {
>  			if (slot->id == id)
>  				continue;
>  			if (!((base_gfn + npages <= slot->base_gfn) ||
>  			      (base_gfn >= slot->base_gfn + slot->npages)))
> -				goto out;
> +				return -EEXIST;
>  		}
>  	}
>  
> -	r = -ENOMEM;
> -
>  	/* Allocate/free page dirty bitmap as needed */
>  	if (!(new.flags & KVM_MEM_LOG_DIRTY_PAGES))
>  		new.dirty_bitmap = NULL;
>  	else if (!new.dirty_bitmap) {
> -		if (kvm_create_dirty_bitmap(&new) < 0)
> -			goto out;
> +		r = kvm_create_dirty_bitmap(&new);
> +		if (r)
> +			return r;
>  	}
>  
>  	slots = kvzalloc(sizeof(struct kvm_memslots), GFP_KERNEL_ACCOUNT);
> -	if (!slots)
> +	if (!slots) {
> +		r = -ENOMEM;
>  		goto out_bitmap;
> +	}
>  	memcpy(slots, __kvm_memslots(kvm, as_id), sizeof(struct kvm_memslots));
>  
>  	if ((change == KVM_MR_DELETE) || (change == KVM_MR_MOVE)) {
> @@ -1068,7 +1065,6 @@ int __kvm_set_memory_region(struct kvm *kvm,
>  out_bitmap:
>  	if (new.dirty_bitmap && !old.dirty_bitmap)
>  		kvm_destroy_dirty_bitmap(&new);
> -out:
>  	return r;
>  }
>  EXPORT_SYMBOL_GPL(__kvm_set_memory_region);
> 

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