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Wed, 7 Jul 2021 08:56:53 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6AE52AE065; Wed, 7 Jul 2021 08:56:53 +0000 (GMT) Received: from li-7e0de7cc-2d9d-11b2-a85c-de26c016e5ad.ibm.com (unknown [9.171.25.185]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 7 Jul 2021 08:56:53 +0000 (GMT) Subject: Re: [PATCH] KVM: s390: Enable specification exception interpretation To: Christian Borntraeger , Janis Schoetterl-Glausch , Janosch Frank , Heiko Carstens , Vasily Gorbik Cc: David Hildenbrand , Cornelia Huck , Claudio Imbrenda , "open list:KERNEL VIRTUAL MACHINE for s390 (KVM/s390)" , "open list:S390" , open list References: <20210706114714.3936825-1-scgl@linux.ibm.com> <05430c91-6a84-0fc9-0af4-89f408eb691f@de.ibm.com> From: Janis Schoetterl-Glausch Message-ID: Date: Wed, 7 Jul 2021 10:56:53 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <05430c91-6a84-0fc9-0af4-89f408eb691f@de.ibm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: y2QuoV-bDBKUBRBZOvJTecMlZ_IeZtTK X-Proofpoint-ORIG-GUID: K1PIvK5-ynjtwKjZ4THaCwQglsXQ-oig X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.391,18.0.790 definitions=2021-07-07_05:2021-07-06,2021-07-07 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 mlxscore=0 lowpriorityscore=0 clxscore=1015 mlxlogscore=999 phishscore=0 priorityscore=1501 spamscore=0 malwarescore=0 adultscore=0 bulkscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2107070047 Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 7/7/21 10:30 AM, Christian Borntraeger wrote: > > > On 06.07.21 13:47, Janis Schoetterl-Glausch wrote: >> When this feature is enabled the hardware is free to interpret >> specification exceptions generated by the guest, instead of causing >> program interruption interceptions. >> >> This benefits (test) programs that generate a lot of specification >> exceptions (roughly 4x increase in exceptions/sec). >> >> Interceptions will occur as before if ICTL_PINT is set, >> i.e. if guest debug is enabled. > > I think I will add > > There is no indication if this feature is available or not and the hardware > is free to interpret or not. So we can simply set this bit and if the > hardware ignores it we fall back to intercept 8 handling. Might also mention vSIE and/or incorporate into first paragraph: When this feature is enabled the hardware is free to interpret specification exceptions generated by the guest, instead of causing program interruption interceptions, but it is not required to. There is no indication if this feature is available or not, so we can simply set this bit and if the hardware ignores it we fall back to intercept 8 handling. The same applies to vSIE, we forward the guest hypervisor's bit and fall back to injection if interpretation does not occur. > > > With that > > Reviewed-by: Christian Borntraeger [...]