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

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Date:	Wed, 11 May 2016 12:35:42 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Laurent Vivier <lvivier@...hat.com>, kvm@...r.kernel.org,
	kvm-ppc@...r.kernel.org
Cc:	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Gleb Natapov <gleb@...nel.org>, linuxppc-dev@...ts.ozlabs.org,
	Paolo Bonzini <pbonzini@...hat.com>,
	Paul Mackerras <paulus@...ba.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm-pr: manage illegal instructions

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@...hat.com>
> ---
>   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?


Alex