Re: [PATCH kvmtool v1 3/5] Use kvm_userspace_memory_region2 for all memory registration

[Alexandru Elisei <alexandru.elisei@arm.com>]

Hi Fuad, Suzuki,

On Mon, Jul 06, 2026 at 11:23:47AM +0100, Suzuki K Poulose wrote:
> Hi Fuad
> 
> On 06/07/2026 09:35, Fuad Tabba wrote:
> > Switch kvm__register_mem() and kvm__destroy_mem() from
> > kvm_userspace_memory_region to kvm_userspace_memory_region2 and
> > KVM_SET_USER_MEMORY_REGION2 unconditionally. The v2 struct is a
> > superset; when the extra fields are zero, the ioctl behaves
> > identically to v1.
> 
> Doesn't this break using this on older KVM implementations ? Not that I
> care, but do others care ?

I haven't had the time to review the series, but I do care about this
change, I find myself from time to time testing old kernels.

I think the two ioctls can coexist without much maintenance burden. For
example, the usage of KVM_SET_USER_MEMORY_REGION can be kept as-is and
KVM_SET_USER_MEMORY_REGION2 can be used only for guest_memfd in
kvm__register_mem().

Thoughts?

Thanks,
Alex

> 
> Cheers
> Suzuki
> 
> 	
> > 
> > This prepares for adding guest_memfd support.
> > 
> > Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
> > ---
> >   kvm.c | 11 +++++------
> >   1 file changed, 5 insertions(+), 6 deletions(-)
> > 
> > diff --git a/kvm.c b/kvm.c
> > index 95ccfcb..8a7fd09 100644
> > --- a/kvm.c
> > +++ b/kvm.c
> > @@ -189,7 +189,7 @@ core_exit(kvm__exit);
> >   int kvm__destroy_mem(struct kvm *kvm, u64 guest_phys, u64 size,
> >   		     void *userspace_addr)
> >   {
> > -	struct kvm_userspace_memory_region mem;
> > +	struct kvm_userspace_memory_region2 mem;
> >   	struct kvm_mem_bank *bank;
> >   	int ret;
> > @@ -213,14 +213,14 @@ int kvm__destroy_mem(struct kvm *kvm, u64 guest_phys, u64 size,
> >   		goto out;
> >   	}
> > -	mem = (struct kvm_userspace_memory_region) {
> > +	mem = (struct kvm_userspace_memory_region2) {
> >   		.slot			= bank->slot,
> >   		.guest_phys_addr	= guest_phys,
> >   		.memory_size		= 0,
> >   		.userspace_addr		= (unsigned long)userspace_addr,
> >   	};
> > -	ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION, &mem);
> > +	ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION2, &mem);
> >   	if (ret < 0) {
> >   		ret = -errno;
> >   		goto out;
> > @@ -239,7 +239,6 @@ out:
> >   int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size,
> >   		      void *userspace_addr, enum kvm_mem_type type)
> >   {
> > -	struct kvm_userspace_memory_region mem;
> >   	struct kvm_mem_bank *merged = NULL;
> >   	struct kvm_mem_bank *bank;
> >   	struct list_head *prev_entry;
> > @@ -320,7 +319,7 @@ int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size,
> >   		flags |= KVM_MEM_READONLY;
> >   	if (type != KVM_MEM_TYPE_RESERVED) {
> > -		mem = (struct kvm_userspace_memory_region) {
> > +		struct kvm_userspace_memory_region2 mem = {
> >   			.slot			= slot,
> >   			.flags			= flags,
> >   			.guest_phys_addr	= guest_phys,
> > @@ -328,7 +327,7 @@ int kvm__register_mem(struct kvm *kvm, u64 guest_phys, u64 size,
> >   			.userspace_addr		= (unsigned long)userspace_addr,
> >   		};
> > -		ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION, &mem);
> > +		ret = ioctl(kvm->vm_fd, KVM_SET_USER_MEMORY_REGION2, &mem);
> >   		if (ret < 0) {
> >   			ret = -errno;
> >   			goto out;
>