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Wed, 7 Jul 2021 08:59:30 +0000 (GMT) Received: from d06av26.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A5F14AE075; Wed, 7 Jul 2021 08:59:29 +0000 (GMT) Received: from oc7455500831.ibm.com (unknown [9.171.89.68]) by d06av26.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 7 Jul 2021 08:59:29 +0000 (GMT) Subject: Re: [PATCH] KVM: s390: Enable specification exception interpretation To: Janis Schoetterl-Glausch , 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: Christian Borntraeger Message-ID: Date: Wed, 7 Jul 2021 10:59:29 +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: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: XiT2ViL0tcCvvtdlW1Ov_7g-1PF_Ks8G X-Proofpoint-ORIG-GUID: cktgOo6vzzu3BV6wCwqJK--5ejhcKKLc 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 lowpriorityscore=0 mlxscore=0 bulkscore=0 spamscore=0 adultscore=0 priorityscore=1501 impostorscore=0 suspectscore=0 phishscore=0 malwarescore=0 clxscore=1015 mlxlogscore=999 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2104190000 definitions=main-2107070050 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07.07.21 10:56, Janis Schoetterl-Glausch wrote: > 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. Can you maybe resend a v2 with all comments (and RBs) added?