Re: [PATCH v8 1/2] target/arm: kvm: Handle DABT with no valid ISS

[Beata Michalska]

On Mon, 29 Jun 2020 at 09:15, Andrew Jones <drjones@redhat.com> wrote:
>
> On Sun, Jun 28, 2020 at 04:04:58PM +0100, Beata Michalska wrote:
> > On ARMv7 & ARMv8 some load/store instructions might trigger a data abort
> > exception with no valid ISS info to be decoded. The lack of decode info
> > makes it at least tricky to emulate those instruction which is one of the
> > (many) reasons why KVM will not even try to do so.
> >
> > Add support for handling those by requesting KVM to inject external
> > dabt into the quest.
> >
> > Signed-off-by: Beata Michalska <beata.michalska@linaro.org>
> > ---
> >  target/arm/kvm.c | 57 
> > +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 56 insertions(+), 1 deletion(-)
> >
> > diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> > index eef3bbd..2dd8a9a 100644
> > --- a/target/arm/kvm.c
> > +++ b/target/arm/kvm.c
> > @@ -39,6 +39,7 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] 
> > = {
> >
> >  static bool cap_has_mp_state;
> >  static bool cap_has_inject_serror_esr;
> > +static bool cap_has_inject_ext_dabt;
> >
> >  static ARMHostCPUFeatures arm_host_cpu_features;
> >
> > @@ -245,6 +246,16 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
> >          ret = -EINVAL;
> >      }
> >
> > +    if (kvm_check_extension(s, KVM_CAP_ARM_NISV_TO_USER)) {
> > +        if (kvm_vm_enable_cap(s, KVM_CAP_ARM_NISV_TO_USER, 0)) {
> > +            error_report("Failed to enable KVM_CAP_ARM_NISV_TO_USER cap");
> > +        } else {
> > +            /* Set status for supporting the external dabt injection */
> > +            cap_has_inject_ext_dabt = kvm_check_extension(s,
> > +                                    KVM_CAP_ARM_INJECT_EXT_DABT);
> > +        }
> > +    }
> > +
> >      return ret;
> >  }
> >
> > @@ -810,6 +821,45 @@ void kvm_arm_vm_state_change(void *opaque, int 
> > running, RunState state)
> >      }
> >  }
> >
> > +/**
> > + * kvm_arm_handle_dabt_nisv:
> > + * @cs: CPUState
> > + * @esr_iss: ISS encoding (limited) for the exception from Data Abort
> > + *           ISV bit set to '0b0' -> no valid instruction syndrome
> > + * @fault_ipa: faulting address for the synchronous data abort
> > + *
> > + * Returns: 0 if the exception has been handled, < 0 otherwise
> > + */
> > +static int kvm_arm_handle_dabt_nisv(CPUState *cs, uint64_t esr_iss,
> > +                             uint64_t fault_ipa)
>
> The indent of 'uint64_t fault_ipa' is off. Should be under CPUState.
>
> > +{
> > +    /*
> > +     * Request KVM to inject the external data abort into the guest
> > +     */
> > +    if (cap_has_inject_ext_dabt) {
> > +        struct kvm_vcpu_events events = { };
> > +        /*
> > +         * The external data abort event will be handled immediately by KVM
> > +         * using the address fault that triggered the exit on given VCPU.
> > +         * Requesting injection of the external data abort does not rely
> > +         * on any other VCPU state. Therefore, in this particular case, 
> > the VCPU
> > +         * synchronization can be exceptionally skipped.
> > +         */
> > +        events.exception.ext_dabt_pending = 1;
> > +        /*
> > +         * KVM_CAP_ARM_INJECT_EXT_DABT implies KVM_CAP_VCPU_EVENTS
> > +         */
>
> Single line comments may be done with /* ... */
>
> > +        return kvm_vcpu_ioctl(cs, KVM_SET_VCPU_EVENTS, &events);
> > +
>
> Extra blank line here.
>
> > +    } else {
> > +        error_report("Data abort exception triggered by guest memory 
> > access "
> > +                     "at physical address: 0x"  TARGET_FMT_lx,
> > +                     (target_ulong)fault_ipa);
> > +        error_printf("KVM unable to emulate faulting instruction.\n");
> > +    }
> > +    return -1;
> > +}
> > +
> >  int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> >  {
> >      int ret = 0;
> > @@ -820,7 +870,12 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run 
> > *run)
> >              ret = EXCP_DEBUG;
> >          } /* otherwise return to guest */
> >          break;
> > -    default:
> > +    case KVM_EXIT_ARM_NISV:
> > +        /* External DABT with no valid iss to decode */
> > +        ret = kvm_arm_handle_dabt_nisv(cs, run->arm_nisv.esr_iss,
> > +                                       run->arm_nisv.fault_ipa);
> > +        break;
> > +     default:
>
> An extra space got added in front of 'default:'
>
> >          qemu_log_mask(LOG_UNIMP, "%s: un-handled exit reason %d\n",
> >                        __func__, run->exit_reason);
> >          break;
> > --
> > 2.7.4
> >
> >
>
> Besides the format changes
>
> Reviewed-by: Andrew Jones <drjones@redhat.com>
>
Done.
Thanks a lot for the reviews!

BR
Beata