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Date: Mon, 10 Jan 2022 17:36:07 +1000
From: Nicholas Piggin <npiggin@gmail.com>
Subject: Re: [PATCH v3 5/6] KVM: PPC: mmio: Return to guest after emulation
 failure
To: Fabiano Rosas <farosas@linux.ibm.com>, kvm-ppc@vger.kernel.org
References: <20220107210012.4091153-1-farosas@linux.ibm.com>
 <20220107210012.4091153-6-farosas@linux.ibm.com>
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Excerpts from Fabiano Rosas's message of January 8, 2022 7:00 am:
> If MMIO emulation fails we don't want to crash the whole guest by
> returning to userspace.
>=20
> The original commit bbf45ba57eae ("KVM: ppc: PowerPC 440 KVM
> implementation") added a todo:
>=20
>   /* XXX Deliver Program interrupt to guest. */
>=20
> 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.
>=20
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  arch/powerpc/kvm/powerpc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>=20
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 6daeea4a7de1..56b0faab7a5f 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -309,7 +309,7 @@ int kvmppc_emulate_mmio(struct kvm_vcpu *vcpu)
>  		kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
>  		kvmppc_core_queue_program(vcpu, 0);
>  		pr_info("%s: emulation failed (%08x)\n", __func__, last_inst);
> -		r =3D RESUME_HOST;
> +		r =3D RESUME_GUEST;

So at this point can the pr_info just go away?

I wonder if this shouldn't be a DSI rather than a program check.=20
DSI with DSISR[37] looks a bit more expected. Not that Linux
probably does much with it but at least it would give a SIGBUS
rather than SIGILL.

Thanks,
Nick

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Nicholas Piggin <npiggin@gmail.com>
Date: Mon, 10 Jan 2022 07:36:07 +0000
Subject: Re: [PATCH v3 5/6] KVM: PPC: mmio: Return to guest after emulation failure
Message-Id: <1641799578.6dxlxsaaos.astroid@bobo.none>
List-Id: <kvm-ppc.vger.kernel.org>
References: <20220107210012.4091153-1-farosas@linux.ibm.com>
 <20220107210012.4091153-6-farosas@linux.ibm.com>
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To: Fabiano Rosas <farosas@linux.ibm.com>, kvm-ppc@vger.kernel.org
Cc: aik@ozlabs.ru, linuxppc-dev@lists.ozlabs.org

Excerpts from Fabiano Rosas's message of January 8, 2022 7:00 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.
> 
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  arch/powerpc/kvm/powerpc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
> index 6daeea4a7de1..56b0faab7a5f 100644
> --- a/arch/powerpc/kvm/powerpc.c
> +++ b/arch/powerpc/kvm/powerpc.c
> @@ -309,7 +309,7 @@ int kvmppc_emulate_mmio(struct kvm_vcpu *vcpu)
>  		kvmppc_get_last_inst(vcpu, INST_GENERIC, &last_inst);
>  		kvmppc_core_queue_program(vcpu, 0);
>  		pr_info("%s: emulation failed (%08x)\n", __func__, last_inst);
> -		r = RESUME_HOST;
> +		r = RESUME_GUEST;

So at this point can the pr_info just go away?

I wonder if this shouldn't be a DSI rather than a program check. 
DSI with DSISR[37] looks a bit more expected. Not that Linux
probably does much with it but at least it would give a SIGBUS
rather than SIGILL.

Thanks,
Nick