| Message ID | 20230721120046.2262291-2-iii@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | KVM: s390: interrupt: Fix stepping into interrupt handlers | expand |
On 21.07.23 13:57, Ilya Leoshkevich wrote: > After single-stepping an instruction that generates an interrupt, GDB > ends up on the second instruction of the respective interrupt handler. > > The reason is that vcpu_pre_run() manually delivers the interrupt, and > then __vcpu_run() runs the first handler instruction using the > CPUSTAT_P flag. This causes a KVM_SINGLESTEP exit on the second handler > instruction. > > Fix by delaying the KVM_SINGLESTEP exit until after the manual > interrupt delivery. > > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> > --- > arch/s390/kvm/interrupt.c | 10 ++++++++++ > arch/s390/kvm/kvm-s390.c | 4 ++-- > 2 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c > index 9bd0a873f3b1..2cebe4227b8e 100644 > --- a/arch/s390/kvm/interrupt.c > +++ b/arch/s390/kvm/interrupt.c > @@ -1392,6 +1392,7 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu) > { > struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int; > int rc = 0; > + bool delivered = false; > unsigned long irq_type; > unsigned long irqs; > > @@ -1465,6 +1466,15 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu) > WARN_ONCE(1, "Unknown pending irq type %ld", irq_type); > clear_bit(irq_type, &li->pending_irqs); > } > + delivered |= !rc; > + } > + Can we add a comment like /* * We delivered at least one interrupt and modified the PC. Force a * singlestep event now. */ > + if (delivered && guestdbg_sstep_enabled(vcpu)) { > + struct kvm_debug_exit_arch *debug_exit = &vcpu->run->debug.arch; > + > + debug_exit->addr = vcpu->arch.sie_block->gpsw.addr; > + debug_exit->type = KVM_SINGLESTEP; > + vcpu->guest_debug |= KVM_GUESTDBG_EXIT_PENDING; > } I do wonder if we, instead, want to do this whenever we modify the PSW. That way we could catch any PC changes and only have to add checks for guestdbg_exit_pending(). But this is simpler and should work as well. Acked-by: David Hildenbrand <david@redhat.com>
On Mon, 2023-07-24 at 10:22 +0200, David Hildenbrand wrote: > On 21.07.23 13:57, Ilya Leoshkevich wrote: > > After single-stepping an instruction that generates an interrupt, > > GDB > > ends up on the second instruction of the respective interrupt > > handler. > > > > The reason is that vcpu_pre_run() manually delivers the interrupt, > > and > > then __vcpu_run() runs the first handler instruction using the > > CPUSTAT_P flag. This causes a KVM_SINGLESTEP exit on the second > > handler > > instruction. > > > > Fix by delaying the KVM_SINGLESTEP exit until after the manual > > interrupt delivery. > > > > Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> > > --- > > arch/s390/kvm/interrupt.c | 10 ++++++++++ > > arch/s390/kvm/kvm-s390.c | 4 ++-- > > 2 files changed, 12 insertions(+), 2 deletions(-) [...] > > Can we add a comment like > > /* > * We delivered at least one interrupt and modified the PC. Force a > * singlestep event now. > */ Ok, will do. > > + if (delivered && guestdbg_sstep_enabled(vcpu)) { > > + struct kvm_debug_exit_arch *debug_exit = &vcpu- > > >run->debug.arch; > > + > > + debug_exit->addr = vcpu->arch.sie_block->gpsw.addr; > > + debug_exit->type = KVM_SINGLESTEP; > > + vcpu->guest_debug |= KVM_GUESTDBG_EXIT_PENDING; > > } > > I do wonder if we, instead, want to do this whenever we modify the > PSW. > > That way we could catch any PC changes and only have to add checks > for > guestdbg_exit_pending(). Wouldn't this break a corner case where the first instruction of the interrupt handler causes the same interrupt? > But this is simpler and should work as well. > > Acked-by: David Hildenbrand <david@redhat.com>
On 24.07.23 10:42, Ilya Leoshkevich wrote: > On Mon, 2023-07-24 at 10:22 +0200, David Hildenbrand wrote: >> On 21.07.23 13:57, Ilya Leoshkevich wrote: >>> After single-stepping an instruction that generates an interrupt, >>> GDB >>> ends up on the second instruction of the respective interrupt >>> handler. >>> >>> The reason is that vcpu_pre_run() manually delivers the interrupt, >>> and >>> then __vcpu_run() runs the first handler instruction using the >>> CPUSTAT_P flag. This causes a KVM_SINGLESTEP exit on the second >>> handler >>> instruction. >>> >>> Fix by delaying the KVM_SINGLESTEP exit until after the manual >>> interrupt delivery. >>> >>> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> >>> --- >>> arch/s390/kvm/interrupt.c | 10 ++++++++++ >>> arch/s390/kvm/kvm-s390.c | 4 ++-- >>> 2 files changed, 12 insertions(+), 2 deletions(-) > > [...] >> > >> Can we add a comment like >> >> /* >> * We delivered at least one interrupt and modified the PC. Force a >> * singlestep event now. >> */ > > Ok, will do. > >>> + if (delivered && guestdbg_sstep_enabled(vcpu)) { >>> + struct kvm_debug_exit_arch *debug_exit = &vcpu- >>>> run->debug.arch; >>> + >>> + debug_exit->addr = vcpu->arch.sie_block->gpsw.addr; >>> + debug_exit->type = KVM_SINGLESTEP; >>> + vcpu->guest_debug |= KVM_GUESTDBG_EXIT_PENDING; >>> } >> >> I do wonder if we, instead, want to do this whenever we modify the >> PSW. >> >> That way we could catch any PC changes and only have to add checks >> for >> guestdbg_exit_pending(). > > Wouldn't this break a corner case where the first instruction of the > interrupt handler causes the same interrupt? Could be, there are many possible corner cases (PGM interrupt at the first instruction of PGM interrupt handler -- our PSW address might not even change)
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c index 9bd0a873f3b1..2cebe4227b8e 100644 --- a/arch/s390/kvm/interrupt.c +++ b/arch/s390/kvm/interrupt.c @@ -1392,6 +1392,7 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu) { struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int; int rc = 0; + bool delivered = false; unsigned long irq_type; unsigned long irqs; @@ -1465,6 +1466,15 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu) WARN_ONCE(1, "Unknown pending irq type %ld", irq_type); clear_bit(irq_type, &li->pending_irqs); } + delivered |= !rc; + } + + if (delivered && guestdbg_sstep_enabled(vcpu)) { + struct kvm_debug_exit_arch *debug_exit = &vcpu->run->debug.arch; + + debug_exit->addr = vcpu->arch.sie_block->gpsw.addr; + debug_exit->type = KVM_SINGLESTEP; + vcpu->guest_debug |= KVM_GUESTDBG_EXIT_PENDING; } set_intercept_indicators(vcpu); diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index d1e768bcfe1d..0c6333b108ba 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -4611,7 +4611,7 @@ static int vcpu_pre_run(struct kvm_vcpu *vcpu) if (!kvm_is_ucontrol(vcpu->kvm)) { rc = kvm_s390_deliver_pending_interrupts(vcpu); - if (rc) + if (rc || guestdbg_exit_pending(vcpu)) return rc; } @@ -4738,7 +4738,7 @@ static int __vcpu_run(struct kvm_vcpu *vcpu) do { rc = vcpu_pre_run(vcpu); - if (rc) + if (rc || guestdbg_exit_pending(vcpu)) break; kvm_vcpu_srcu_read_unlock(vcpu);
After single-stepping an instruction that generates an interrupt, GDB ends up on the second instruction of the respective interrupt handler. The reason is that vcpu_pre_run() manually delivers the interrupt, and then __vcpu_run() runs the first handler instruction using the CPUSTAT_P flag. This causes a KVM_SINGLESTEP exit on the second handler instruction. Fix by delaying the KVM_SINGLESTEP exit until after the manual interrupt delivery. Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com> --- arch/s390/kvm/interrupt.c | 10 ++++++++++ arch/s390/kvm/kvm-s390.c | 4 ++-- 2 files changed, 12 insertions(+), 2 deletions(-)