Re: [PATCH v1 2/5] KVM: s390: vsie: Fix delivery of addressing exceptions

Christian Borntraeger
2020-04-06T13:18:13Z

On 02.04.20 20:48, David Hildenbrand wrote:
> Whenever we get an -EFAULT, we failed to read in guest 2 physical
> address space. Such addressing exceptions are reported via a program
> intercept to the nested hypervisor.
>
> We faked the intercept, we have to return to guest 2. Instead, right
> now we would be returning -EFAULT from the intercept handler, eventually
> crashing the VM.
>
> Addressing exceptions can only happen if the g2->g3 page tables
> reference invalid g2 addresses (say, either a table or the final page is
> not accessible - so something that basically never happens in sane
> environments.
>
> Identified by manual code inspection.
>
> Fixes: a3508fbe9dc6 ("KVM: s390: vsie: initial support for nested virtualization")
> Cc: <stable@vger.kernel.org> # v4.8+
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> arch/s390/kvm/vsie.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 076090f9e666..4f6c22d72072 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -1202,6 +1202,7 @@ static int vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> scb_s->iprcc = PGM_ADDRESSING;
> scb_s->pgmilc = 4;
> scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4);
> + rc = 1;

kvm_s390_handle_vsie has

return rc < 0 ? rc : 0;

so rc = 0 would result in the same behaviour, correct?
Since we DO handle everything as we should, why rc = 1 ?