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Message-ID: <af7be3a9-816c-95dc-22a7-cf62fe245e24@redhat.com>
Date: Mon, 24 Jul 2023 10:22:52 +0200
From: David Hildenbrand <david@...hat.com>
To: Ilya Leoshkevich <iii@...ux.ibm.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>,
Heiko Carstens <hca@...ux.ibm.com>,
Vasily Gorbik <gor@...ux.ibm.com>,
Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: Sven Schnelle <svens@...ux.ibm.com>, kvm@...r.kernel.org,
linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
Jens Freimann <jfreimann@...hat.com>
Subject: Re: [PATCH v2 1/6] KVM: s390: interrupt: Fix single-stepping into
interrupt handlers
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@...ux.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@...hat.com>
--
Cheers,
David / dhildenb
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