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    Subject[PATCH 4.9 036/125] KVM: s390: vsie: Fix delivery of addressing exceptions
    Date
    From: David Hildenbrand <david@redhat.com>

    commit 4d4cee96fb7a3cc53702a9be8299bf525be4ee98 upstream.

    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.
    the correct thing to do is to return 1 as rc == 1 is the internal
    representation of "we have to go back into g2".

    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>
    Link: https://lore.kernel.org/r/20200403153050.20569-3-david@redhat.com
    Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
    Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
    [borntraeger@de.ibm.com: fix patch description]
    Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/s390/kvm/vsie.c | 1 +
    1 file changed, 1 insertion(+)

    --- a/arch/s390/kvm/vsie.c
    +++ b/arch/s390/kvm/vsie.c
    @@ -947,6 +947,7 @@ static int vsie_run(struct kvm_vcpu *vcp
    scb_s->iprcc = PGM_ADDRESSING;
    scb_s->pgmilc = 4;
    scb_s->gpsw.addr = __rewind_psw(scb_s->gpsw, 4);
    + rc = 1;
    }
    return rc;
    }

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