Re: [PATCH] KVM: PPC: Fix illegal opcode emulation in kvm-pr

[Alexander Graf <agraf@suse.de>]

On 05/19/2016 09:58 AM, Laurent Vivier wrote:
>
> On 18/05/2016 21:01, Thomas Huth wrote:
>> If kvmppc_handle_exit_pr() calls kvmppc_emulate_instruction() to emulate
>> one instruction (in the BOOK3S_INTERRUPT_H_EMUL_ASSIST case), it calls
>> kvmppc_core_queue_program() afterwards if kvmppc_emulate_instruction()
>> returned EMULATE_FAIL, so the guest gets an program interrupt for the
>> illegal opcode.
>> However, the kvmppc_emulate_instruction() also tried to inject a
>> program exception for this already, so the program interrupt gets
>> injected twice and the return address in srr0 gets destroyed.
>> All other callers of kvmppc_emulate_instruction() are also injecting
>> a program interrupt, and since the callers have the right knowledge
>> about the srr1 flags that should be used, it is the function
>> kvmppc_emulate_instruction() that should _not_ inject program
>> interrupts, so remove the kvmppc_core_queue_program() here.
>>
>> This fixes the issue discovered by Laurent Vivier with kvm-unit-tests
>> where the logs are filled with these messages when the test tries
>> to execute an illegal instruction:
>>
>>       Couldn't emulate instruction 0x00000000 (op 0 xop 0)
>>       kvmppc_handle_exit_pr: emulation at 700 failed (00000000)
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>   arch/powerpc/kvm/emulate.c | 1 -
>>   1 file changed, 1 deletion(-)
>>
>> diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c
>> index 5cc2e7a..b379146 100644
>> --- a/arch/powerpc/kvm/emulate.c
>> +++ b/arch/powerpc/kvm/emulate.c
>> @@ -302,7 +302,6 @@ int kvmppc_emulate_instruction(struct kvm_run *run, struct kvm_vcpu *vcpu)
>>   			advance = 0;
>>   			printk(KERN_ERR "Couldn't emulate instruction 0x%08x "
>>   			       "(op %d xop %d)\n", inst, get_op(inst), get_xop(inst));
>> -			kvmppc_core_queue_program(vcpu, 0);
>>   		}
>>   	}
>>   
>>
> I've tested this patch with kvm-unit-tests: it solves the multiple
> illegal instruction exceptions, but the test fails because SRR1 is not
> updated correctly. It should contains the bit for "Illegal Instruction"
> whereas it is 0.
> [But I think it's what you explain in your last email]

So if the illegal instruction flag is missing, that's probably because 
the host CPU didn't pass that in via SRR1. That's probably a subtle 
difference between EMUL_ASSIST and PROGRAM.

Please send a follow-up patch that sets the illegal instruction bit in 
flags on EMULATE_FAIL as well.


Alex