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Mon, 14 Mar 2022 10:02:41 +0000 (GMT) Received: from [9.145.181.26] (unknown [9.145.181.26]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Mon, 14 Mar 2022 10:02:41 +0000 (GMT) Message-ID: <0a39b94c-db5e-a8cc-b84b-ae17559f1091@linux.ibm.com> Date: Mon, 14 Mar 2022 11:02:40 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH v2 3/9] KVM: s390: pv: Add query interface Content-Language: en-US To: Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, david@redhat.com, borntraeger@linux.ibm.com References: <20220310103112.2156-1-frankja@linux.ibm.com> <20220310103112.2156-4-frankja@linux.ibm.com> <20220311184059.25161d62@p-imbrenda> From: Janosch Frank In-Reply-To: <20220311184059.25161d62@p-imbrenda> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: vcweE2HlHSvN2iAEYQwyV8uSXkyoKeSk X-Proofpoint-ORIG-GUID: xXVuM66vRdzC1vTg4mnzbWaUbD-YRAU5 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.816,Hydra:6.0.425,FMLib:17.11.64.514 definitions=2022-03-14_04,2022-03-11_02,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 impostorscore=0 mlxscore=0 mlxlogscore=999 suspectscore=0 bulkscore=0 lowpriorityscore=0 spamscore=0 adultscore=0 clxscore=1015 phishscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2203140065 Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On 3/11/22 18:40, Claudio Imbrenda wrote: > On Thu, 10 Mar 2022 10:31:06 +0000 > Janosch Frank wrote: > >> Some of the query information is already available via sysfs but >> having a IOCTL makes the information easier to retrieve. > > if I understand correctly, this will be forward-compatible but not > backwards compatible. > > you return the amount of bytes written into the buffer, but only if the > buffer was already big enough. > > a newer userspace will work with an older kernel, but an older > userspace will not work with a newer kernel. I expect the first version of userspace to request a minimum length hence I return -EINVAL if less space is given. In the future the minimum will be a constant and we'll write between the min and the new data length. IMHO there's no sense in allowing to request less data than the v1 of the interface will provide. > > a solution would be to return the size of the struct, so userspace can > know how much of the buffer was written (if it was bigger than the > struct), or that there are unwritten bits (if the buffer was smaller). > > and even if the buffer was too small, write back as much of it as > possible to userspace. > > this way, an older userspace will get the information it expects. > > > I am also not a big fan of writing the size in the input struct (I think > returning it would be cleaner), but I do not have a strong opinion > >> >> Signed-off-by: Janosch Frank >> --- >> arch/s390/kvm/kvm-s390.c | 76 ++++++++++++++++++++++++++++++++++++++++ >> include/uapi/linux/kvm.h | 25 +++++++++++++ >> 2 files changed, 101 insertions(+) >> >> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c >> index 020356653d1a..67e1e445681f 100644 >> --- a/arch/s390/kvm/kvm-s390.c >> +++ b/arch/s390/kvm/kvm-s390.c >> @@ -2224,6 +2224,42 @@ static int kvm_s390_cpus_to_pv(struct kvm *kvm, u16 *rc, u16 *rrc) >> return r; >> } >> >> +/* >> + * Here we provide user space with a direct interface to query UV >> + * related data like UV maxima and available features as well as >> + * feature specific data. >> + * >> + * To facilitate future extension of the data structures we'll try to >> + * write data up to the maximum requested length. >> + */ >> +static ssize_t kvm_s390_handle_pv_info(struct kvm_s390_pv_info *info) >> +{ >> + ssize_t len; >> + >> + switch (info->header.id) { >> + case KVM_PV_INFO_VM: { >> + len = sizeof(info->header) + sizeof(info->vm); >> + >> + if (info->header.len_max < 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 len; >> + } >> + default: >> + return -EINVAL; >> + } >> +} >> + >> static int kvm_s390_handle_pv(struct kvm *kvm, struct kvm_pv_cmd *cmd) >> { >> int r = 0; >> @@ -2360,6 +2396,46 @@ 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 = {}; >> + ssize_t data_len; >> + >> + /* >> + * No need to check the VM protection here. >> + * >> + * Maybe user space wants to query some of the data >> + * when the VM is still unprotected. If we see the >> + * need to fence a new data command we can still >> + * return an error in the info handler. >> + */ >> + >> + r = -EFAULT; >> + if (copy_from_user(&info, argp, sizeof(info.header))) >> + break; >> + >> + r = -EINVAL; >> + if (info.header.len_max < sizeof(info.header)) >> + break; >> + >> + data_len = kvm_s390_handle_pv_info(&info); >> + if (data_len < 0) { >> + r = data_len; >> + break; >> + } >> + /* >> + * If a data command struct is extended (multiple >> + * times) this can be used to determine how much of it >> + * is valid. >> + */ >> + info.header.len_written = data_len; >> + >> + r = -EFAULT; >> + if (copy_to_user(argp, &info, data_len)) >> + break; >> + >> + r = 0; >> + break; >> + } >> default: >> r = -ENOTTY; >> } >> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h >> index a02bbf8fd0f6..21f19863c417 100644 >> --- a/include/uapi/linux/kvm.h >> +++ b/include/uapi/linux/kvm.h >> @@ -1643,6 +1643,30 @@ 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_max; >> + __u32 len_written; >> + __u32 reserved; >> +}; >> + >> +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, >> @@ -1651,6 +1675,7 @@ enum pv_cmd_id { >> KVM_PV_VERIFY, >> KVM_PV_PREP_RESET, >> KVM_PV_UNSHARE_ALL, >> + KVM_PV_INFO, >> }; >> >> struct kvm_pv_cmd { >