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

Janosch Frank
2022-03-02T09:03:36Z

On 3/1/22 18:32, Claudio Imbrenda wrote:
> 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

I'd like to avoid having to rely on reading more files. IOCTLs are the
most used way to communicate with KVM and don't require larger changes
to QEMU.

This is information that's meant for the VMM so in this case KVM can
control what it reports. If I'd add a raw interface then we can't
control what's being passed to userspace.

Btw. the UV driver by Steffen provides raw QUI data but we can't
guarantee that it will always be available to QEMU.

>
>>>
>>> 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 {
>>
>