Re: [PATCH] kvm-pr: manage illegal instructions

[Alexander Graf]

On 05/11/2016 01:14 PM, Laurent Vivier wrote:
> On 11/05/2016 12:35, Alexander Graf wrote:
> > On 03/15/2016 09:18 PM, Laurent Vivier wrote:
> > > While writing some instruction tests for kvm-unit-tests for powerpc,
> > > I've found that illegal instructions are not managed correctly with
> > > kvm-pr,
> > > while it is fine with kvm-hv.
> > >
> > > When an illegal instruction (like ".long 0") is processed by kvm-pr,
> > > the kernel logs are filled with:
> > >
> > >        Couldn't emulate instruction 0x00000000 (op 0 xop 0)
> > >        kvmppc_handle_exit_pr: emulation at 700 failed (00000000)
> > >
> > > While the exception handler receives an interrupt for each instruction
> > > executed after the illegal instruction.
> > >
> > > Signed-off-by: Laurent Vivier <lvivier@xxxxxxxxxx>
> > > ---
> > >    arch/powerpc/kvm/book3s_emulate.c | 4 +++-
> > >    1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/arch/powerpc/kvm/book3s_emulate.c
> > > b/arch/powerpc/kvm/book3s_emulate.c
> > > index 2afdb9c..4ee969d 100644
> > > --- a/arch/powerpc/kvm/book3s_emulate.c
> > > +++ b/arch/powerpc/kvm/book3s_emulate.c
> > > @@ -99,7 +99,6 @@ int kvmppc_core_emulate_op_pr(struct kvm_run *run,
> > > struct kvm_vcpu *vcpu,
> > >          switch (get_op(inst)) {
> > >        case 0:
> > > -        emulated = EMULATE_FAIL;
> > >            if ((kvmppc_get_msr(vcpu) & MSR_LE) &&
> > >                (inst == swab32(inst_sc))) {
> > >                /*
> > > @@ -112,6 +111,9 @@ int kvmppc_core_emulate_op_pr(struct kvm_run *run,
> > > struct kvm_vcpu *vcpu,
> > >                kvmppc_set_gpr(vcpu, 3, EV_UNIMPLEMENTED);
> > >                kvmppc_set_pc(vcpu, kvmppc_get_pc(vcpu) + 4);
> > >                emulated = EMULATE_DONE;
> > > +        } else {
> > > +            kvmppc_core_queue_program(vcpu, SRR1_PROGILL);
> > But isn't that exactly what the semantic of EMULATE_FAIL is? Fixing it
> > up in book3s_emulate.c is definitely the wrong spot.
> >
> > So what is the problem you're trying to solve? Is the SRR0 at the wrong
> > spot or are the log messages the problem?
> No, the problem is the host kernel logs are filled by the message and
> the execution hangs. And the host becomes unresponsiveness, even after
> the end of the tests.
>
> Please, try to run kvm-unit-tests (the emulator test) on a KVM-PR host,
> and check the kernel logs (dmesg), then try to ssh to the host...

Ok, so the log messages are the problem. Please fix the message output 
then - or remove it altogether. Or if you like, create a module 
parameter that allows you to emit them.

I personally think the best solution would be to just convert the 
message into a trace point.

While at it, please see whether the guest can trigger similar host log 
output excess in other code paths.


Alex