Commit f71d0dc5 authored Mar 18, 2014 by David Hildenbrand Committed by Christian Borntraeger Apr 22, 2014

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 <dahi@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

parent bb78c5ec

arch/s390/kvm/guestdbg.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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;

arch/s390/kvm/interrupt.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -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;
		}

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