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Mon, 6 Jul 2026 11:30:20 +0000 (GMT) Message-ID: <721266da-db8f-4385-87c1-ca26c430892c@linux.ibm.com> Date: Mon, 6 Jul 2026 13:30:20 +0200 Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 19/27] s390: Introduce Start Arm Execution instruction To: Janosch Frank , Steffen Eiden , kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Cc: Alexander Gordeev , Andreas Grapentin , Arnd Bergmann , Catalin Marinas , Claudio Imbrenda , David Hildenbrand , Friedrich Welter , Gautam Gala , Hariharan Mari , Heiko Carstens , Hendrik Brueckner , Ilya Leoshkevich , Joey Gouly , Marc Zyngier , Nico Boehr , Nina Schoetterl-Glausch , Oliver Upton , Paolo Bonzini , Suzuki K Poulose , Sven Schnelle , Ulrich Weigand , Vasily Gorbik , Will Deacon , Zenghui Yu References: <20260706085229.979525-1-seiden@linux.ibm.com> <20260706085229.979525-20-seiden@linux.ibm.com> <8239c9ba-154c-4e2d-b2fc-700ba12eb585@linux.ibm.com> Content-Language: en-US From: Christian Borntraeger In-Reply-To: <8239c9ba-154c-4e2d-b2fc-700ba12eb585@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA2MDExNCBTYWx0ZWRfXyXs5OGzOANhv ZIJl81eEuRU4Cpez+mW/Cv4V3PCkqB38qFKziSlSUv/NThQ82C72diIb9Sg7BPrUytroTklEQsh TXffBA8Sqc3nex38XAZ12ERM3F6nJHk= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA2MDExNCBTYWx0ZWRfX8V1IkIBid673 qSMlAej2yF6fkd6r8CLZG47k77Z39HY4Wbz3MHH24E9KroifQ+EGG9Rl10MhEzQ+DkOjyGmpUn/ N0NVi6v/TeoISNhYhibPdltRcdAwNMZWgoYDz0X088HeeYbx/DVp86me0g9ALzEo/PNeK/C/TG5 BlolhKbNKhUGP4HdLyzzie+RkWHVQHzFoCYMw3n0oNC7ogTYe0dAm0zc159bAEUzS0vd32+7qvG EUOnm8UZPuWYfBU5h1uKyl2QlIDIUIgA8IRJjkcOh0FOaOeaHb+3giJbUpEFLAf6bpXsPT27naY uZIg7RGcfaVDDn6l0AYJpqHT5yFl9S5K6SMAA6JiEEcFcELatJ8TuGt5HBtPvDm09SUkDe0Dd29 Z94ldvwtp8kDGD/786wPpipS/It78xwWX7M3bkoeUr+tDQfa9xPVA+/bcCTXkJeI/WPT5i38jVz EJRDSvywjkaz63XzHLw== X-Proofpoint-GUID: QO9Jmrtl9YbmYkeOKN-Rxs6ZbudI9ERe X-Authority-Analysis: v=2.4 cv=Oot/DS/t c=1 sm=1 tr=0 ts=6a4b91d5 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=02lCwkMJHSWm-2F3BxgA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: QO9Jmrtl9YbmYkeOKN-Rxs6ZbudI9ERe X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-06_01,2026-07-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 lowpriorityscore=0 clxscore=1011 impostorscore=0 phishscore=0 malwarescore=0 suspectscore=0 spamscore=0 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607060114 Am 06.07.26 um 13:17 schrieb Janosch Frank: >> +SYM_FUNC_START(__sae64a) >> +    stmg    %r6,%r14,__SF_GPRS(%r15)    # store kernel registers >> +    STBEAR    __SF_SAE_BEAR(%r15)        # save breaking event address register >> +    .insn    rre,0xb9a50000,%r2,0        # Start Arm Execution >> +# Let the next instruction be NOP to avoid triggering a machine check >> +# and handling it in a guest as result of the instruction execution. > > @Christian: > I have the feeling things got lost in translation when this comment was written. > How would we trigger a MCHECK by having an instruction after SIE/SAE? > AFAIU this allows us to have a label which we can check in the mcheck handler to decide who triggered the mcheck. the original rationale was that some machine checks are nullifying some are terminating. So the PSW might point to SAE or the instruction afterwards for a guest machine check. In SIE, we use that nop to account any machine check on that nop as a guest machine check. > > Without the label the comment and NOP are useless as far as I can see. > So we need to decide if this still applies and then either remove it or add sae handling to mcck_int_handler and maybe other mcheck functions. We plan to get more information on the machine checks for sae so we might no longer need that. But this series does not yet contain the machine check handling. Maybe its better to remove comment and nop and introduce that later when we add machine check handling and if still needed.