Hi,
On Mon, 23 Mar 2020 at 12:44, Andrew Jones <drjones@xxxxxxxxxx> wrote:
>
> On Mon, Mar 23, 2020 at 11:32:26AM +0000, 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@xxxxxxxxxx>
> > ---
> > target/arm/cpu.h | 2 ++
> > target/arm/kvm.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > target/arm/kvm_arm.h | 11 +++++++++++
> > 3 files changed, 67 insertions(+)
> >
> > diff --git a/target/arm/cpu.h b/target/arm/cpu.h
> > index 4ffd991..4f834c1 100644
> > --- a/target/arm/cpu.h
> > +++ b/target/arm/cpu.h
> > @@ -560,6 +560,8 @@ typedef struct CPUARMState {
> > uint64_t esr;
> > } serror;
> >
> > + uint8_t ext_dabt_pending; /* Request for injecting ext DABT */
> > +
> > /* State of our input IRQ/FIQ/VIRQ/VFIQ lines */
> > uint32_t irq_line_state;
> >
> > diff --git a/target/arm/kvm.c b/target/arm/kvm.c
> > index 85860e6..c088589 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;
> >
> > @@ -244,6 +245,16 @@ 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)) {
> > + warn_report("Failed to enable DABT NISV cap");
>
> Shouldn't this be an error? If KVM says it has KVM_CAP_ARM_NISV_TO_USER,
> then I think it should always work to enable it, unless userspace passes
> the wrong flags. Currently flags must be zero, but if they were to change
> then we'll need to add the flags to vmstate and fail migration when they
> aren't compatible, and I guess that failure would occur here.
>
That's a fair point. From the kernel point of view this one is pretty
straightforward,
so it should not fail. I haven't used the error here as the lack of
this cap is not really
critical for guest but indeed it might be worth to have it here .
> > + } 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;
> > }
> >
> > @@ -703,9 +714,16 @@ int kvm_put_vcpu_events(ARMCPU *cpu)
> > events.exception.serror_esr = env->serror.esr;
> > }
> >
> > + if (cap_has_inject_ext_dabt) {
> > + events.exception.ext_dabt_pending = env->ext_dabt_pending;
> > + }
> > +
> > ret = kvm_vcpu_ioctl(CPU(cpu), KVM_SET_VCPU_EVENTS, &events);
> > if (ret) {
> > error_report("failed to put vcpu events");
> > + } else {
> > + /* Clear instantly if the call was successful */
> > + env->ext_dabt_pending = 0;
> > }
> >
> > return ret;
> > @@ -819,6 +837,11 @@ int kvm_arch_handle_exit(CPUState *cs, struct kvm_run *run)
> > ret = EXCP_DEBUG;
> > } /* otherwise return to guest */
> > break;
> > + 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:
> > qemu_log_mask(LOG_UNIMP, "%s: un-handled exit reason %d\n",
> > __func__, run->exit_reason);
> > @@ -953,3 +976,34 @@ int kvm_arch_msi_data_to_gsi(uint32_t data)
> > {
> > return (data - 32) & 0xffff;
> > }
> > +
> > +int kvm_arm_handle_dabt_nisv(CPUState *cs, uint64_t esr_iss,
> > + uint64_t fault_ipa)
> > +{
> > + ARMCPU *cpu = ARM_CPU(cs);
> > + CPUARMState *env = &cpu->env;
> > +
> > + /*
> > + * ISS [23:14] is invalid so there is a limited info
> > + * on what has just happened so the only *useful* thing that can
> > + * be retrieved from ISS is WnR & DFSC (though in some cases WnR
> > + * might be less of a value as well)
> > + */
> > +
> > + /*
> > + * Set pending ext dabt and trigger SET_EVENTS so that
> > + * KVM can inject the abort
> > + */
> > + if (cap_has_inject_ext_dabt) {
> > + kvm_cpu_synchronize_state(cs);
>
> I guess this is just an expensive 'vcpu_dirty=true', which the comment
> above justifies, but not super clearly. Can you try to clarify the
> comment some more? I also wonder if we shouldn't add a KVM function
> that just marks a vcpu dirty, rather than fetching all registers.
>
I can definitely adjust the comments here to explain the case more
clearly. And I would definitely vote for moving the flag
setting/clearing outside the
sync so that it can be triggered separately without involving all the series
of potentially unnecessary ioctls. WIll draft that in the next iteration.
Thanks
Beata
> > + env->ext_dabt_pending = 1;
> > + } 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;
> > + }
> > +
> > + return 0;
> > +}
> > diff --git a/target/arm/kvm_arm.h b/target/arm/kvm_arm.h
> > index ae9e075..39472d5 100644
> > --- a/target/arm/kvm_arm.h
> > +++ b/target/arm/kvm_arm.h
> > @@ -450,6 +450,17 @@ struct kvm_guest_debug_arch;
> > void kvm_arm_copy_hw_debug_data(struct kvm_guest_debug_arch *ptr);
> >
> > /**
> > + * 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 synch data abort
> > + *
> > + * Returns: 0 if the exception has been handled, < 0 otherwise
> > + */
> > +int kvm_arm_handle_dabt_nisv(CPUState *cs, uint64_t esr_iss,
> > + uint64_t fault_ipa);
> > +/**
> > * its_class_name:
> > *
> > * Return the ITS class name to use depending on whether KVM acceleration
> > --
> > 2.7.4
> >
>
> Thanks,
> drew
>
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