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Wed, 6 May 2026 14:50:52 +0000 (GMT) Received: from [9.61.249.171] (unknown [9.61.249.171]) by smtpav05.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 6 May 2026 14:50:52 +0000 (GMT) Message-ID: Date: Wed, 6 May 2026 10:50:52 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 3/4] KVM: s390: Change the fi->lock to a raw_spinlock for RT case To: Heiko Carstens Cc: borntraeger@linux.ibm.com, imbrenda@linux.ibm.com, frankja@linux.ibm.com, david@kernel.org, gor@linux.ibm.com, agordeev@linux.ibm.com, svens@linux.ibm.com, kvm@vger.kernel.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, mjrosato@linux.ibm.com References: <20260505173728.160562-1-freimuth@linux.ibm.com> <20260505173728.160562-4-freimuth@linux.ibm.com> <20260506045734.11230A02-hca@linux.ibm.com> Content-Language: en-US From: Douglas Freimuth In-Reply-To: <20260506045734.11230A02-hca@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-ORIG-GUID: foTD0CRPasax-PbCZ_SrJMF1kD0N3KDn X-Proofpoint-GUID: foTD0CRPasax-PbCZ_SrJMF1kD0N3KDn X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTA2MDE0NCBTYWx0ZWRfX+3AohF6DDMaY FopO4Wg2NqL70tqiN6lnBFKyuBQtqzi2hdAOwC+/GuOejrTzhAebj8znhc5sDR9R+xkDUH35vHy TlTRLfmzjQAoStpXkvPjhwrMojjzBQXyVWnZ7jpmBX1Ew5xRvFcOf2CHsmbkRMMZXkeqccb3zqA 1BEfQOo+5l6o4eqWZd3WUeuKU9aRmSe8uXlOCPBYPcQ5Ng5qk8ATZFaozkisUCOY4OKHfe7YXij PV1ZjC1YVCN6Ts8gbRt7Om63V8SzGVzocboFDGdqp3gFcnAbbBq5sgwMB27bcAckOPkKiMst421 yZNLXoO3L2y52J1U5Wxgkkwhh1goDCuawiF4f4KfOvxqFgUb2QTItktrrY77VlUwjmZX5bsO5wQ BYgyyCzoV0RPJ+wlsXZK4Gl4TGTUJ4Maumi3eQJZtPsG5nZUXP09oLf3RY/mpeQs4JpBS406zdh LXzyygpbehycnWC/4Bw== X-Authority-Analysis: v=2.4 cv=UbFhjqSN c=1 sm=1 tr=0 ts=69fb5550 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=ljoCnXVPeUkr4m1FovgA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-05-05_03,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 spamscore=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 adultscore=0 priorityscore=1501 bulkscore=0 phishscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605060144 On 5/6/26 12:57 AM, Heiko Carstens wrote: > On Tue, May 05, 2026 at 07:37:27PM +0200, Douglas Freimuth wrote: >> s390 needs to maintain support for an RT kernel. This requires the >> floating interrupt lock, fi->lock to be changed to a raw spin lock >> since the fi->lock maybe called with interrupts disabled in __inject_io. >> >> Signed-off-by: Douglas Freimuth >> --- >> arch/s390/include/asm/kvm_host.h | 2 +- >> arch/s390/kvm/intercept.c | 4 +- >> arch/s390/kvm/interrupt.c | 68 ++++++++++++++++---------------- >> arch/s390/kvm/kvm-s390.c | 2 +- >> 4 files changed, 38 insertions(+), 38 deletions(-) > > s390 does not support RT, but I guess you are referring to a lockdep splat > which you would see without doing this change, similar like we have seen at > other places. > > Can you include the relevant parts of the splat for reference, please? Heiko, thank you for you response. I dont recall trapping it with lockdep (while it was on) but discussion on the mailing list in an earlier version made us look closer (and we saw it across the AI models that reviewed the patch.) It appears that while RT isn't supported it can still be compiled in to the kernel so we wanted to mitigate the issues we would add to if someone does that while not impacting non-RT environments, the main use case.