KVM: s390: hardware support for guest debugging

This patch adds support to debug the guest using the PER facility on s390.
Single-stepping, hardware breakpoints and hardware watchpoints are supported. In
order to use the PER facility of the guest without it noticing it, the control
registers of the guest have to be patched and access to them has to be
intercepted(stctl, stctg, lctl, lctlg).

All PER program interrupts have to be intercepted and only the relevant PER
interrupts for the guest have to be given back. Special care has to be taken
about repeated exits on the same hardware breakpoint. The intervention of the
host in the guests PER configuration is not fully transparent. PER instruction
nullification can not be used by the guest and too many storage alteration
events may be reported to the guest (if it is activated for special address
ranges only) when the host concurrently debugging it.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
index c0e6b49191ba..f61c800a2d2c 100644
--- a/arch/s390/kvm/intercept.c
+++ b/arch/s390/kvm/intercept.c
@@ -170,6 +170,8 @@ static void __extract_prog_irq(struct kvm_vcpu *vcpu,
 	}
 }
 
+#define per_event(vcpu) (vcpu->arch.sie_block->iprcc & PGM_PER)
+
 static int handle_prog(struct kvm_vcpu *vcpu)
 {
 	struct kvm_s390_pgm_info pgm_info;
@@ -178,6 +180,13 @@ static int handle_prog(struct kvm_vcpu *vcpu)
 
 	vcpu->stat.exit_program_interruption++;
 
+	if (guestdbg_enabled(vcpu) && per_event(vcpu)) {
+		kvm_s390_handle_per_event(vcpu);
+		/* the interrupt might have been filtered out completely */
+		if (vcpu->arch.sie_block->iprcc == 0)
+			return 0;
+	}
+
 	/* Restore ITDB to Program-Interruption TDB in guest memory */
 	if (!IS_TE_ENABLED(vcpu) || !IS_ITDB_VALID(vcpu))
 		goto skip_itdb;