Re: [PATCH 3/9] KVM: s390: pv: Add query interface

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Wed, 23 Feb 2022 12:30:36 +0100
Thomas Huth <thuth@redhat.com> wrote:

> On 23/02/2022 10.20, Janosch Frank wrote:
> > Some of the query information is already available via sysfs but
> > having a IOCTL makes the information easier to retrieve.

why not exporting this via sysfs too?

something like a sysfs file called "query_ultravisor_information_raw"

that way you don't even have a problem with sizes

> > 
> > Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> > ---
> >   arch/s390/kvm/kvm-s390.c | 47 ++++++++++++++++++++++++++++++++++++++++
> >   include/uapi/linux/kvm.h | 23 ++++++++++++++++++++
> >   2 files changed, 70 insertions(+)
> > 
> > diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> > index faa85397b6fb..837f898ad2ff 100644
> > --- a/arch/s390/kvm/kvm-s390.c
> > +++ b/arch/s390/kvm/kvm-s390.c
> > @@ -2217,6 +2217,34 @@ static int kvm_s390_cpus_to_pv(struct kvm *kvm, u16 *rc, u16 *rrc)
> >   	return r;
> >   }
> >   
> > +static int kvm_s390_handle_pv_info(struct kvm_s390_pv_info *info)
> > +{
> > +	u32 len;
> > +
> > +	switch (info->header.id) {
> > +	case KVM_PV_INFO_VM: {
> > +		len =  sizeof(info->header) + sizeof(info->vm);
> > +
> > +		if (info->header.len < len)
> > +			return -EINVAL;
> > +
> > +		memcpy(info->vm.inst_calls_list,
> > +		       uv_info.inst_calls_list,
> > +		       sizeof(uv_info.inst_calls_list));
> > +
> > +		/* It's max cpuidm not max cpus so it's off by one */
> > +		info->vm.max_cpus = uv_info.max_guest_cpu_id + 1;
> > +		info->vm.max_guests = uv_info.max_num_sec_conf;
> > +		info->vm.max_guest_addr = uv_info.max_sec_stor_addr;
> > +		info->vm.feature_indication = uv_info.uv_feature_indications;
> > +
> > +		return 0;
> > +	}
> > +	default:
> > +		return -EINVAL;
> > +	}
> > +}
> > +
> >   static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
> >   {
> >   	int r = 0;
> > @@ -2353,6 +2381,25 @@ static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd)
> >   			     cmd->rc, cmd->rrc);
> >   		break;
> >   	}
> > +	case KVM_PV_INFO: {
> > +		struct kvm_s390_pv_info info = {};
> > +
> > +		if (copy_from_user(&info, argp, sizeof(info.header)))
> > +			return -EFAULT;
> > +
> > +		if (info.header.len < sizeof(info.header))
> > +			return -EINVAL;
> > +
> > +		r = kvm_s390_handle_pv_info(&info);
> > +		if (r)
> > +			return r;
> > +
> > +		r = copy_to_user(argp, &info, sizeof(info));  
> 
> sizeof(info) is currently OK ... but this might break if somebody later 
> extends the kvm_s390_pv_info struct, I guess? ==> Maybe also better use 
> sizeof(info->header) + sizeof(info->vm) here, too? Or let 
> kvm_s390_handle_pv_info() return the amount of bytes that should be copied here?
> 
>   Thomas
> 
> 
> > +		if (r)
> > +			return -EFAULT;
> > +		return 0;
> > +	}
> >   	default:
> >   		r = -ENOTTY;
> >   	}
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index dbc550bbd9fa..96fceb204a92 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -1642,6 +1642,28 @@ struct kvm_s390_pv_unp {
> >   	__u64 tweak;
> >   };
> >   
> > +enum pv_cmd_info_id {
> > +	KVM_PV_INFO_VM,
> > +};
> > +
> > +struct kvm_s390_pv_info_vm {
> > +	__u64 inst_calls_list[4];
> > +	__u64 max_cpus;
> > +	__u64 max_guests;
> > +	__u64 max_guest_addr;
> > +	__u64 feature_indication;
> > +};
> > +
> > +struct kvm_s390_pv_info_header {
> > +	__u32 id;
> > +	__u32 len;
> > +};
> > +
> > +struct kvm_s390_pv_info {
> > +	struct kvm_s390_pv_info_header header;
> > +	struct kvm_s390_pv_info_vm vm;
> > +};
> > +
> >   enum pv_cmd_id {
> >   	KVM_PV_ENABLE,
> >   	KVM_PV_DISABLE,
> > @@ -1650,6 +1672,7 @@ enum pv_cmd_id {
> >   	KVM_PV_VERIFY,
> >   	KVM_PV_PREP_RESET,
> >   	KVM_PV_UNSHARE_ALL,
> > +	KVM_PV_INFO,
> >   };
> >   
> >   struct kvm_pv_cmd {  
>