From f71d0dc5084b4de761b5be1aef1a855136cecd15 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Tue, 18 Mar 2014 10:06:14 +0100 Subject: [PATCH] KVM: s390: no timer interrupts when single-stepping a guest When a guest is single-stepped, we want to disable timer interrupts. Otherwise, the guest will continuously execute the external interrupt handler and make debugging of code where timer interrupts are enabled almost impossible. The delivery of timer interrupts can be enforced in such sections by setting a breakpoint and continuing execution. In order to disable timer interrupts, they are disabled in the control register of the guest just before SIE entry and are suppressed in the interrupt check/delivery methods. Signed-off-by: David Hildenbrand Reviewed-by: Cornelia Huck Signed-off-by: Christian Borntraeger --- arch/s390/kvm/guestdbg.c | 2 ++ arch/s390/kvm/interrupt.c | 3 +++ 2 files changed, 5 insertions(+) diff --git a/arch/s390/kvm/guestdbg.c b/arch/s390/kvm/guestdbg.c index 100e99d1030d..757ccef62fd5 100644 --- a/arch/s390/kvm/guestdbg.c +++ b/arch/s390/kvm/guestdbg.c @@ -155,6 +155,8 @@ void kvm_s390_patch_guest_per_regs(struct kvm_vcpu *vcpu) */ if (guestdbg_sstep_enabled(vcpu)) { + /* disable timer (clock-comparator) interrupts */ + vcpu->arch.sie_block->gcr[0] &= ~0x800ul; vcpu->arch.sie_block->gcr[9] |= PER_EVENT_IFETCH; vcpu->arch.sie_block->gcr[10] = 0; vcpu->arch.sie_block->gcr[11] = PSW_ADDR_INSN; diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c index 0165f1b089ac..d020c5f8eabb 100644 --- a/arch/s390/kvm/interrupt.c +++ b/arch/s390/kvm/interrupt.c @@ -61,6 +61,9 @@ static int ckc_interrupts_enabled(struct kvm_vcpu *vcpu) if (psw_extint_disabled(vcpu) || !(vcpu->arch.sie_block->gcr[0] & 0x800ul)) return 0; + if (guestdbg_enabled(vcpu) && guestdbg_sstep_enabled(vcpu)) + /* No timer interrupts when single stepping */ + return 0; return 1; } -- 2.30.2