Re: [PATCH 1/2] KVM: guest_memfd: Return -EEXIST for overlapping bindings

[Sean Christopherson <seanjc@google.com>]

On Mon, May 18, 2026, ZongYao.Chen@linux.alibaba.com wrote:
> From: Zongyao Chen <ZongYao.Chen@linux.alibaba.com>
> 
> KVM_SET_USER_MEMORY_REGION2 rejects guest_memfd ranges that overlap an
> existing binding, but kvm_gmem_bind() currently reports the failure through
> its generic -EINVAL path.  That makes binding conflicts indistinguishable
> from malformed guest_memfd parameters.
> 
> Return -EEXIST when the target guest_memfd range is already bound, matching
> the errno used for overlapping GPA memslots and making the two types of
> range conflicts report the same class of error to userspace.

The other key piece of information is that we quite clearly intended to return
-EEXIST in this case, given the testcase, but simply failed on multiple fronts.

No need for a v2, I'll add a blurb when applying.

> Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
> Signed-off-by: Zongyao Chen <ZongYao.Chen@linux.alibaba.com>
> ---
>  virt/kvm/guest_memfd.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 69c9d6d546b2..46727539d08a 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -675,6 +675,7 @@ int kvm_gmem_bind(struct kvm *kvm, struct kvm_memory_slot *slot,
>  
>  	if (!xa_empty(&f->bindings) &&
>  	    xa_find(&f->bindings, &start, end - 1, XA_PRESENT)) {
> +		r = -EEXIST;
>  		filemap_invalidate_unlock(inode->i_mapping);
>  		goto err;
>  	}
> -- 
> 2.47.3
>