Re: [PATCH v3 2/6] KVM: s390: interrupt: Fix single-stepping into program interrupt handlers

Claudio Imbrenda
2023-07-25T13:53:44Z

On Mon, 24 Jul 2023 11:44:08 +0200
Ilya Leoshkevich <iii@linux.ibm.com> wrote:

> Currently, after single-stepping an instruction that generates a
> specification exception, GDB ends up on the instruction immediately
> following it.
>
> The reason is that vcpu_post_run() injects the interrupt and sets
> KVM_GUESTDBG_EXIT_PENDING, causing a KVM_SINGLESTEP exit. The
> interrupt is not delivered, however, therefore userspace sees the
> address of the next instruction.
>
> Fix by letting the __vcpu_run() loop go into the next iteration,
> where vcpu_pre_run() delivers the interrupt and sets
> KVM_GUESTDBG_EXIT_PENDING.
>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
> arch/s390/kvm/intercept.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/kvm/intercept.c b/arch/s390/kvm/intercept.c
> index 954d39adf85c..7cdd927541b0 100644
> --- a/arch/s390/kvm/intercept.c
> +++ b/arch/s390/kvm/intercept.c
> @@ -226,7 +226,22 @@ static int handle_itdb(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> -#define per_event(vcpu) (vcpu->arch.sie_block->iprcc & PGM_PER)
> +static bool should_handle_per_event(const struct kvm_vcpu *vcpu)
> +{
> + if (!guestdbg_enabled(vcpu))
> + return false;
> + if (!(vcpu->arch.sie_block->iprcc & PGM_PER))

why not if (!per_event(vcpu)) ?

maybe you can even merge it with the previous if:

if (!guestdbg_enabled(vcpu) || !per_event(vcpu))
return false;

this is closer to the old code too

> + return false;
> + if (guestdbg_sstep_enabled(vcpu) &&
> + vcpu->arch.sie_block->iprcc != PGM_PER) {
> + /*
> + * __vcpu_run() will exit after delivering the concurrently
> + * indicated condition.
> + */
> + return false;
> + }
> + return true;
> +}
>
> static int handle_prog(struct kvm_vcpu *vcpu)
> {
> @@ -242,7 +257,7 @@ static int handle_prog(struct kvm_vcpu *vcpu)
> if (kvm_s390_pv_cpu_is_protected(vcpu))
> return -EOPNOTSUPP;
>
> - if (guestdbg_enabled(vcpu) && per_event(vcpu)) {
> + if (should_handle_per_event(vcpu)) {
> rc = kvm_s390_handle_per_event(vcpu);
> if (rc)
> return rc;