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Mon, 4 Mar 2024 08:44:55 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id AE18C20040; Mon, 4 Mar 2024 08:44:53 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C6D3F20043; Mon, 4 Mar 2024 08:44:52 +0000 (GMT) Received: from [9.179.29.223] (unknown [9.179.29.223]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 4 Mar 2024 08:44:52 +0000 (GMT) Message-ID: <1deb0e32-7351-45d2-a342-96a659402be8@linux.ibm.com> Date: Mon, 4 Mar 2024 09:44:52 +0100 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] KVM: s390: vsie: retry SIE instruction on host intercepts To: David Hildenbrand , Eric Farman , Janosch Frank , Claudio Imbrenda Cc: kvm@vger.kernel.org, linux-s390@vger.kernel.org, Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Sven Schnelle References: <20240301204342.3217540-1-farman@linux.ibm.com> <338544a6-4838-4eeb-b1b2-2faa6c11c1be@redhat.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <338544a6-4838-4eeb-b1b2-2faa6c11c1be@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: Q-faGH8MRRb-NEBinXG1H99z4wZ6YX_o X-Proofpoint-GUID: 82YXLDNHXmBEZ8e5v0pvQFFJzrJ8n8hy X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-03-04_04,2024-03-01_03,2023-05-22_02 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 priorityscore=1501 adultscore=0 phishscore=0 lowpriorityscore=0 spamscore=0 impostorscore=0 mlxlogscore=629 bulkscore=0 clxscore=1015 mlxscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2403040066 Am 04.03.24 um 09:35 schrieb David Hildenbrand: > On 01.03.24 21:43, Eric Farman wrote: >> It's possible that SIE exits for work that the host needs to perform >> rather than something that is intended for the guest. >> >> A Linux guest will ignore this intercept code since there is nothing >> for it to do, but a more robust solution would rewind the PSW back to >> the SIE instruction. This will transparently resume the guest once >> the host completes its work, without the guest needing to process >> what is effectively a NOP and re-issue SIE itself. > > I recall that 0-intercepts are valid by the architecture. Further, I recall that there were some rather tricky corner cases where avoiding 0-intercepts would not be that easy. > > Now, it's been a while ago, and maybe I misremember. SoI'm trusting people with access to documentation can review this. Yes, 0-intercepts are allowed, and this also happens when LPAR has an exit. So this patch is not necessary, the question is if this would be an valuable optimization?