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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: jxGEgPZYUe_F3FGPy4bHIWgJYym3cEaI X-Proofpoint-GUID: bGscq2jGxlTGgPr9k4vRQrKHJUg1Zke4 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.680,FMLib:17.12.28.16 definitions=2024-07-03_09,2024-07-03_01,2024-05-17_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 mlxlogscore=334 mlxscore=0 priorityscore=1501 impostorscore=0 malwarescore=0 phishscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.19.0-2406140001 definitions=main-2407030106 On 4/29/24 12:18, Christian Borntraeger wrote: > Am 04.03.24 um 16:37 schrieb Eric Farman: >> On Mon, 2024-03-04 at 09:44 +0100, Christian Borntraeger wrote: >>> >>> >>> 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. >> >> Any chance you recall any details of those corner cases? I can try to >> chase some of them down. >> >>>> >>>> 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. >> >> From an offline conversation I'd had some months back: >> >> """ >> The arch does allow ICODE=0 to be stored, but it's supposed to happen >> only upon a host interruption -- in which case the old PSW is supposed >> to point back at the SIE, to resume guest execution if the host should >> LPSW oldPSW. >> """ > > Just re-read the architecture again and I agree, the SIE instruction should > be nullified. So we should go forward with this somehow. > > Eric, can you maybe add this to devel for CI coverage so that we see if there > are corner cases? Maybe also try to do some performance things (how many IPIs > can we get in guest2 when a guest3 is running and how many IPIs are possible > in a guest3). > > This patch has had contact with the CI for quite a while and I'm gathering patches. Is this an ack now?