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Wed, 18 May 2022 16:51:37 +0000 (GMT) Message-ID: <5de8d8c2-100d-f935-667c-1090ee31277d@linux.ibm.com> Date: Wed, 18 May 2022 18:55:26 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Subject: Re: [PATCH v9 3/3] s390x: KVM: resetting the Topology-Change-Report Content-Language: en-US To: David Hildenbrand , Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, frankja@linux.ibm.com, cohuck@redhat.com, thuth@redhat.com, hca@linux.ibm.com, gor@linux.ibm.com, wintera@linux.ibm.com, seiden@linux.ibm.com, nrb@linux.ibm.com References: <20220506092403.47406-1-pmorel@linux.ibm.com> <20220506092403.47406-4-pmorel@linux.ibm.com> <76fd0c11-5b9b-0032-183b-54db650f13b1@redhat.com> <20220512115250.2e20bfdf@p-imbrenda> <70a7d93c-c1b1-fa72-0eb4-02e3e2235f94@redhat.com> From: Pierre Morel In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: W5fS3N71cLrX1I_e6-quxj7Z0L_xZDmt X-Proofpoint-GUID: uu-AwpmzG2aQew89jZnaju95wJ-pORKx X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.874,Hydra:6.0.486,FMLib:17.11.64.514 definitions=2022-05-18_06,2022-05-17_02,2022-02-23_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 malwarescore=0 phishscore=0 suspectscore=0 spamscore=0 mlxscore=0 bulkscore=0 priorityscore=1501 mlxlogscore=792 adultscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2202240000 definitions=main-2205180099 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/18/22 16:33, David Hildenbrand wrote: > On 16.05.22 16:21, Pierre Morel wrote: >> >> >> On 5/12/22 12:01, David Hildenbrand wrote: >>>>> >>>>> I think we prefer something like u16 when copying to user space. >>>> >>>> but then userspace also has to expect a u16, right? >>> >>> Yep. >>> >> >> Yes but in fact, inspired by previous discussion I had on the VFIO >> interface, that is the reason why I did prefer an int. >> It is much simpler than a u16 and the definition of a bit. >> >> Despite a bit in a u16 is what the s3990 achitecture proposes I thought >> we could make it easier on the KVM/QEMU interface. >> >> But if the discussion stops here, I will do as you both propose change >> to u16 in KVM and userland and add the documentation for the interface. > > In general, we pass via the ABI fixed-sized values -- u8, u16, u32, u64 > ... instead of int. Simply because sizeof(int) is in theory variable > (e.g., 32bit vs 64bit). > > Take a look at arch/s390/include/uapi/asm/kvm.h and you won't find any > usage of int or bool. > > Having that said, I'll let the maintainers decide. Using e.g., u8 is > just the natural thing to do on a Linux ABI, but we don't really support > 32 bit ... maybe we'll support 128bit at one point? ;) > OK then I use u16 with a flag in case we get something in the utilities which is related to the topology in the future. Thanks, Pierre -- Pierre Morel IBM Lab Boeblingen