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Tue, 1 Sep 2026 11:44:09 +0000 (GMT) Message-ID: Date: Tue, 1 Sep 2026 13:44:09 +0200 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 v2 11/20] KVM: s390: arm64: Query Available Arm features To: sashiko-reviews@lists.linux.dev, Steffen Eiden Cc: Alexander Gordeev , Oliver Upton , kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-s390@vger.kernel.org, Marc Zyngier , Christian Borntraeger , Heiko Carstens , Vasily Gorbik References: <20260831145536.913567-1-seiden@linux.ibm.com> <20260831145536.913567-12-seiden@linux.ibm.com> <20260831194654.39B451F000E9@smtp.kernel.org> Content-Language: en-US From: Janosch Frank Autocrypt: addr=frankja@linux.ibm.com; keydata= xsFNBFubpD4BEADX0uhkRhkj2AVn7kI4IuPY3A8xKat0ihuPDXbynUC77mNox7yvK3X5QBO6 qLqYr+qrG3buymJJRD9xkp4mqgasHdB5WR9MhXWKH08EvtvAMkEJLnqxgbqf8td3pCQ2cEpv 15mH49iKSmlTcJ+PvJpGZcq/jE42u9/0YFHhozm8GfQdb9SOI/wBSsOqcXcLTUeAvbdqSBZe zuMRBivJQQI1esD9HuADmxdE7c4AeMlap9MvxvUtWk4ZJ/1Z3swMVCGzZb2Xg/9jZpLsyQzb lDbbTlEeyBACeED7DYLZI3d0SFKeJZ1SUyMmSOcr9zeSh4S4h4w8xgDDGmeDVygBQZa1HaoL Esb8Y4avOYIgYDhgkCh0nol7XQ5i/yKLtnNThubAcxNyryw1xSstnKlxPRoxtqTsxMAiSekk 0m3WJwvwd1s878HrQNK0orWd8BzzlSswzjNfQYLF466JOjHPWFOok9pzRs+ucrs6MUwDJj0S cITWU9Rxb04XyigY4XmZ8dywaxwi2ZVTEg+MD+sPmRrTw+5F+sU83cUstuymF3w1GmyofgsU Z+/ldjToHnq21MNa1wx0lCEipCCyE/8K9B9bg9pUwy5lfx7yORP3JuAUfCYb8DVSHWBPHKNj HTOLb2g2UT65AjZEQE95U2AY9iYm5usMqaWD39pAHfhC09/7NQARAQABzSVKYW5vc2NoIEZy YW5rIDxmcmFua2phQGxpbnV4LmlibS5jb20+wsF3BBMBCAAhBQJbm6Q+AhsjBQsJCAcCBhUI CQoLAgQWAgMBAh4BAheAAAoJEONU5rjiOLn4p9gQALjkdj5euJVI2nNT3/IAxAhQSmRhPEt0 AmnCYnuTcHRWPujNr5kqgtyER9+EMQ0ZkX44JU2q7OWxTdSNSAN/5Z7qmOR9JySvDOf4d3mS bMB5zxL9d8SbnSs1uW96H9ZBTlTQnmLfsiM9TetAjSrR8nUmjGhe2YUhJLR1v1LguME+YseT eXnLzIzqqpu311/eYiiIGcmaOjPCE+vFjcXL5oLnGUE73qSYiujwhfPCCUK0850o1fUAYq5p CNBCoKT4OddZR+0itKc/cT6NwEDwdokeg0+rAhxb4Rv5oFO70lziBplEjOxu3dqgIKbHbjza EXTb+mr7VI9O4tTdqrwJo2q9zLqqOfDBi7NDvZFLzaCewhbdEpDYVu6/WxprAY94hY3F4trT rQMHJKQENtF6ZTQc9fcT5I3gAmP+OEvDE5hcTALpWm6Z6SzxO7gEYCnF+qGXqp8sJVrweMub UscyLqHoqdZC2UG4LQ1OJ97nzDpIRe0g6oJ9ZIYHKmfw5jjwH6rASTld5MFWajWdNsqK15k/ RZnHAGICKVIBOBsq26m4EsBlfCdt3b/6emuBjUXR1pyjHMz2awWzCq6/6OWs5eANZ0sdosNq dq2v0ULYTazJz2rlCXV89qRa7ukkNwdBSZNEwsD4eEMicj1LSrqWDZMAALw50L4jxaMD7lPL jJbazsFNBFubpD4BEADAcUTRqXF/aY53OSH7IwIK9lFKxIm0IoFkOEh7LMfp7FGzaP7ANrZd cIzhZi38xyOkcaFY+npGEWvko7rlIAn0JpBO4x3hfhmhBD/WSY8LQIFQNNjEm3vzrMo7b9Jb JAqQxfbURY3Dql3GUzeWTG9uaJ00u+EEPlY8zcVShDltIl5PLih20e8xgTnNzx5c110lQSu0 iZv2lAE6DM+2bJQTsMSYiwKlwTuv9LI9Chnoo6+tsN55NqyMxYqJgElk3VzlTXSr3+rtSCwf tq2cinETbzxc1XuhIX6pu/aCGnNfuEkM34b7G1D6CPzDMqokNFbyoO6DQ1+fW6c5gctXg/lZ 602iEl4C4rgcr3+EpfoPUWzKeM8JXv5Kpq4YDxhvbitr8Dm8gr38+UKFZKlWLlwhQ56r/zAU v6LIsm11GmFs2/cmgD1bqBTNHHcTWwWtRTLgmnqJbVisMJuYJt4KNPqphTWsPY8SEtbufIlY HXOJ2lqUzOReTrie2u0qcSvGAbSfec9apTFl2Xko/ddqPcZMpKhBiXmY8tJzSPk3+G4tqur4 6TYAm5ouitJsgAR61Cu7s+PNuq/pTLDhK+6/Njmc94NGBcRA4qTuysEGE79vYWP2oIAU4Fv6 gqaWHZ4MEI2XTqH8wiwzPdCQPYsSE0fXWiYu7ObeErT6iLSTZGx4rQARAQABwsFfBBgBCAAJ BQJbm6Q+AhsMAAoJEONU5rjiOLn4DDEP/RuyckW65SZcPG4cMfNgWxZF8rVjeVl/9PBfy01K 8R0hajU40bWtXSMiby7j0/dMjz99jN6L+AJHJvrLz4qYRzn2Ys843W+RfXj62Zde4YNBE5SL jJweRCbMWKaJLj6499fctxTyeb9+AMLQS4yRSwHuAZLmAb5AyCW1gBcTWZb8ON5BmWnRqeGm IgC1EvCnHy++aBnHTn0m+zV89BhTLTUal35tcjUFwluBY39R2ux/HNlBO1GY3Z+WYXhBvq7q katThLjaQSmnOrMhzqYmdShP1leFTVbzXUUIYv/GbynO/YrL2gaQpaP1bEUEi8lUAfXJbEWG dnHFkciryi092E8/9j89DJg4mmZqOau7TtUxjRMlBcIliXkzSLUk+QvD4LK1kWievJse4mte FBdkWHfP4BH/+8DxapRcG1UAheSnSRQ5LiO50annOB7oXF+vgKIaie2TBfZxQNGAs3RQ+bga DchCqFm5adiSP5+OT4NjkKUeGpBe/aRyQSle/RropTgCi85pje/juYEn2P9UAgkfBJrOHvQ9 Z+2Sva8FRd61NJLkCJ4LFumRn9wQlX2icFbi8UDV3do0hXJRRYTWCxrHscMhkrFWLhYiPF4i phX7UNdOWBQ90qpHyAxHmDazdo27gEjfvsgYMdveKknEOTEb5phwxWgg7BcIDoJf9UMC In-Reply-To: <20260831194654.39B451F000E9@smtp.kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=EIc2FVZC c=1 sm=1 tr=0 ts=6a96ba8e cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=VwQbUJbxAAAA:8 a=H2J1ql-I7Lu3LdE3378A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTAxMDEwMiBTYWx0ZWRfX7Rp5TiDnhW7Z s6tGkTTKphiYFN3rDzD3A4YJANiITqPpDo3HWgJ7OuNy1Z94P/luD8mHjNBxPrBaKo5DAA208If Yxt/+LNPHNejHNlj9PUldGbqrcTi7qLEYYZQWVpeCQ0GnNbke9jOD+fPpFQOmJlLHMgNqYZZfCl 9W+MmNtOr8VIMj3y6v5PRI7Iv+Pg1iDHj5H3sL51XIPIs+d/axutCqINy/KsztJXPwKLw8+ll8A B5syXdk6N+5/QRUUhlmaEsHAKX3lgS9xRL3k137JMuWTPfJq9CIhpyfJr3gSbzKuJn2Pu/LG9fm taMwp323xeXYj5yMLyzTWmDTRKoakBLqlgQKlfk3avR2AqJeI5a1IKsHNSrozseQQRW2HhUUrEQ nuqS+jFV3hly20fScyRRzYllkqbflfYbK4ZDA8hSfRldLaou/0JtjIkHv3e3TVhZJIQ6jr9LgfB Otx2YNMHEUC5TpDKJ9Q== X-Proofpoint-GUID: Tg0JgOrFhG86iz5Frw-Y2jhVn3D-Bx65 X-Proofpoint-ORIG-GUID: Tg0JgOrFhG86iz5Frw-Y2jhVn3D-Bx65 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAxMDEwMiBTYWx0ZWRfX6uotoSvz98jg hrLXAKcZNpJmScHyqLpf/SghfIxEPX4e36BFMj0Di6R2WTFGTg60N4isi+/Sf+LYqXsGb5Qf4uu xCN7+lftNkRnGtWW0BUoiWYrF3qQ3rc= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-01_03,2026-08-31_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 impostorscore=0 suspectscore=0 priorityscore=1501 clxscore=1015 phishscore=0 spamscore=0 adultscore=0 lowpriorityscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609010102 On 8/31/26 9:46 PM, sashiko-bot@kernel.org wrote: > Thank you for your contribution! Sashiko AI review found 4 potential issue(s) to consider: > - [Critical] The EX_TABLE entry in the `qaaf` inline assembly incorrectly places the exception fixup label on the non-faulting `lhi` instruction instead of the potentially faulting `.insn` instruction, which will cause unhandled hardware exceptions to panic the kernel. > - [High] `aef_sysfs_init()` unconditionally calls `aef_init_save_area()`, failing to skip it when the AEF facility is not present, causing a crash on older hardware. > - [High] Off-by-two index error when accessing the QAAF registers array in `kvm_qaaf_read_ftr_reg()`, causing KVM to read incorrect memory offsets for all features. > - [High] If QAAF initialization fails, the global capability flag `info.arm_guest_supp` is not cleared, leading KVM to initialize using uninitialized hardware capability data. > -- [...] >> diff --git a/arch/s390/kernel/aef.c b/arch/s390/kernel/aef.c >> new file mode 100644 >> index 0000000000000..825e2643a8921 >> --- /dev/null >> +++ b/arch/s390/kernel/aef.c > [ ... ] >> +static int __init aef_query_info(void) >> +{ >> + int ret; >> + >> + if (IS_ENABLED(CONFIG_KVM_S390_ARM64)) { >> + info.sae_avail = sclp.has_aef; >> + info.ptff_avail = ptff_query(PTFF_QAGTO) && >> + ptff_query(PTFF_QAGPT); >> + info.arm_guest_supp = info.sae_avail && info.ptff_avail; >> + } >> + if (!info.sae_avail) >> + return 0; >> + >> + ret = qaaf(QAAF_FC_QMC, (union qaaf_block *)&qmc); >> + if (ret) >> + return ret; > > [Severity: High] > If the qaaf instruction fails and returns an error here, `info.arm_guest_supp` > remains set to true. > > Because aef_sysfs_init() is called via an arch_initcall, the initialization > failure is ultimately ignored by the kernel. Later, kvm_s390_arm64_init() > checks `aef_info()->arm_guest_supp` and will proceed to initialize KVM using > the uninitialized `qmc` block. > > Should `info.arm_guest_supp` be cleared before returning when qaaf() fails? No, we can instead check the sclp bit for sae_avail and early return before the assignments. I don't see a gain in having this information shadowed considering the two patchsets that are floating around. Maybe you need it at a later time? sae_avail is also used in patch #20 where it makes even less sense. Either the machine and KVM have sae capabilities or we don't need the sysfs files. So why even add it as a file? It's not like UV where we need to opt in, it's either supported or not. If it's not supported there's no need to have sysfs files. > > [ ... ] >> +static int __init aef_sysfs_init(void) aef_info_init()? >> +{ >> + int rc = -ENOMEM; >> + >> + if (!IS_ENABLED(CONFIG_KVM_S390_ARM64)) >> + return 0; >> + >> + rc = aef_query_info(); >> + if (rc) >> + return rc; >> + >> + rc = aef_init_save_area(); >> + if (rc) >> + return rc; > > [Severity: High] > Will this execute the new qaaf instruction unconditionally on all hardware? > > aef_query_info() correctly returns 0 if the AEF facility is absent (since > `info.sae_avail` would be false). However, aef_init_save_area() is called > immediately after without checking if the facility is actually supported. > > Could this trigger an operation exception on older hardware? >