From: Heiko Carstens Date: Thu, 15 Apr 2021 08:01:27 +0000 (+0200) Subject: KVM: s390: fix guarded storage control register handling X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=44bada28219031f9e8e86b84460606efa57b871e;p=linux.git KVM: s390: fix guarded storage control register handling store_regs_fmt2() has an ordering problem: first the guarded storage facility is enabled on the local cpu, then preemption disabled, and then the STGSC (store guarded storage controls) instruction is executed. If the process gets scheduled away between enabling the guarded storage facility and before preemption is disabled, this might lead to a special operation exception and therefore kernel crash as soon as the process is scheduled back and the STGSC instruction is executed. Fixes: 4e0b1ab72b8a ("KVM: s390: gs support for kvm guests") Signed-off-by: Heiko Carstens Reviewed-by: Christian Borntraeger Reviewed-by: David Hildenbrand Reviewed-by: Janosch Frank Reviewed-by: Cornelia Huck Cc: # 4.12 Link: https://lore.kernel.org/r/20210415080127.1061275-1-hca@linux.ibm.com Signed-off-by: Christian Borntraeger --- diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index cfe720d16a6a9..95ef9193f12e7 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -4313,16 +4313,16 @@ static void store_regs_fmt2(struct kvm_vcpu *vcpu) kvm_run->s.regs.bpbc = (vcpu->arch.sie_block->fpf & FPF_BPBC) == FPF_BPBC; kvm_run->s.regs.diag318 = vcpu->arch.diag318_info.val; if (MACHINE_HAS_GS) { + preempt_disable(); __ctl_set_bit(2, 4); if (vcpu->arch.gs_enabled) save_gs_cb(current->thread.gs_cb); - preempt_disable(); current->thread.gs_cb = vcpu->arch.host_gscb; restore_gs_cb(vcpu->arch.host_gscb); - preempt_enable(); if (!vcpu->arch.host_gscb) __ctl_clear_bit(2, 4); vcpu->arch.host_gscb = NULL; + preempt_enable(); } /* SIE will save etoken directly into SDNX and therefore kvm_run */ }