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Mon, 6 Jul 2026 11:58:19 +0000 (GMT) Date: Mon, 6 Jul 2026 13:58:17 +0200 From: Steffen Eiden To: Christian Borntraeger Cc: Janosch Frank , kvm@vger.kernel.org, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, 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 Subject: Re: [PATCH v4 19/27] s390: Introduce Start Arm Execution instruction Message-ID: <20260706115817.104396-Q-seiden@linux.ibm.com> References: <20260706085229.979525-1-seiden@linux.ibm.com> <20260706085229.979525-20-seiden@linux.ibm.com> <8239c9ba-154c-4e2d-b2fc-700ba12eb585@linux.ibm.com> <721266da-db8f-4385-87c1-ca26c430892c@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <721266da-db8f-4385-87c1-ca26c430892c@linux.ibm.com> X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=Q/XiJY2a c=1 sm=1 tr=0 ts=6a4b9864 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=8nJEP1OIZ-IA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=FTWlFeZUYPafzdOhfvQA:9 a=3ZKOabzyN94A:10 a=wPNLvfGTeEIA:10 X-Proofpoint-GUID: P9k7z7Z_-LJ633J5h5ZAbGS_1o5NSp29 X-Proofpoint-ORIG-GUID: P9k7z7Z_-LJ633J5h5ZAbGS_1o5NSp29 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA2MDEyMCBTYWx0ZWRfX86pjNKnjcEBv O1NRzWszvfaa3PA8qtTL/+y+PePzWaM1r8x16LoGaPRLdmAwbVhoI1m8XgW6n8wlRCI37pP8985 Ji6iI1DvV2kxFN0JUtdutIAez+z40DI= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA2MDEyMCBTYWx0ZWRfXycyknJwSF+9d s22nUFQOtFXZ6AmwRN0W9n/PRaxHVLXKaEcPYiJzNb64Y8UZMRBRgKfFSKLfkgvGQZedtR2/pB2 +1UiEhzN/Cr7ghUZaDXkLW3x1T+RVzpLgAlvSLu2of4XBOOkKTZGw8YN1Wq04aRSDI0+o6CcgcF Lf34IY3kmhxg2vnKd2rMECRSgqqxyXC5hU4iR5xcUT0XlLZuOQWXpoAW8u+1d8tvGGOU9aIS4k/ Q21n45b2zSEqlc9iU5x6SYbFsyd4JB5A6MT4WS9WMMt74mZLhuOVUC+W7JLdH3UfLpHZ8SqjEsI CGcVQq4iJji2cBRtqu5OWKQGiIjS0lCAUmrNknec0vDk+8M6I8dFqCjYg+R3L3az5RpMf+Vw3xn p2xckP5k+7TSqORnSLYGyka9/CnIceFidfl3WJ21jlOfj/5ij9r2NuTzr8oN9vPEKm4gOcEmAOH 26Qq12rBNLKJclH+PaQ== 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 adultscore=0 impostorscore=0 spamscore=0 phishscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607060120 On Mon, Jul 06, 2026 at 01:30:20PM +0200, Christian Borntraeger wrote: > > > 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. Ok I'll remove the comment and the nop for the next round.