Re: [PATCH v4 4/5] KVM: PPC: mmio: Return to guest after emulation failure

[Nicholas Piggin <npiggin@gmail.com>]

Excerpts from Fabiano Rosas's message of January 22, 2022 8:26 am:
> If MMIO emulation fails we don't want to crash the whole guest by
> returning to userspace.
> 
> The original commit bbf45ba57eae ("KVM: ppc: PowerPC 440 KVM
> implementation") added a todo:
> 
>   /* XXX Deliver Program interrupt to guest. */
> 
> and later the commit d69614a295ae ("KVM: PPC: Separate loadstore
> emulation from priv emulation") added the Program interrupt injection
> but in another file, so I'm assuming it was missed that this block
> needed to be altered.
> 
> Also change the message to a ratelimited one since we're letting the
> guest run and it could flood the host logs.
> 
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

One small thing...

> ---
>  arch/powerpc/kvm/powerpc.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 27fb2b70f631..214602c58f13 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -307,9 +307,9 @@ int kvmppc_emulate_mmio(struct kvm_vcpu *vcpu)
>  		u32 last_inst;
>  
>  		kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
> -		/* XXX Deliver Program interrupt to guest. */
> -		pr_emerg("%s: emulation failed (%08x)\n", __func__, last_inst);
> -		r = RESUME_HOST;
> +		pr_info_ratelimited("KVM: guest access to device memory using unsupported instruction (PID: %d opcode: %#08x)\n",
> +				    current->pid, last_inst);

Minor thing but KVM now has some particular printing helpers so I wonder 
if we should start moving to them in general with our messages.

vcpu_debug_ratelimited() maybe?

Thanks,
Nick