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    SubjectRe: [PATCH v6 07/13] KVM: s390: introduce struct kvm_s390_gisa_interrupt
    On Thu, 24 Jan 2019 13:59:33 +0100
    Michael Mueller <mimu@linux.ibm.com> wrote:

    > Use this struct analog to the kvm interruption structs
    > for kvm emulated floating and local interruptions.
    > Further fields will be added with this series as
    > required.
    >
    > Signed-off-by: Michael Mueller <mimu@linux.ibm.com>

    While looking at this I was asking myself what guards against invalid
    gisa pointer dereference e.g. when pending_irqs() is called (see below).

    AFAIU we set up gisa_int.origin only if we have
    css_general_characteristics.aiv. Opinions?

    Anyway if it is a problem, it is a pre-existing one (should be fixed
    ASAP but does not affect the validity of this patch).

    Reviewed-by: Halil Pasic <pasic@linux.ibm.com>

    > ---
    > arch/s390/include/asm/kvm_host.h | 6 ++++-
    > arch/s390/kvm/interrupt.c | 52 +++++++++++++++++++++++-----------------
    > arch/s390/kvm/kvm-s390.c | 2 +-
    > 3 files changed, 36 insertions(+), 24 deletions(-)
    >
    > diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
    > index c259a67c4298..0941571d34eb 100644
    > --- a/arch/s390/include/asm/kvm_host.h
    > +++ b/arch/s390/include/asm/kvm_host.h
    > @@ -803,6 +803,10 @@ struct kvm_s390_vsie {
    > struct page *pages[KVM_MAX_VCPUS];
    > };
    >

    [..]

    > diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
    > index 942cc7d33766..ee91d1de0036 100644
    > --- a/arch/s390/kvm/interrupt.c
    > +++ b/arch/s390/kvm/interrupt.c
    > @@ -246,7 +246,8 @@ static inline unsigned long pending_irqs_no_gisa(struct kvm_vcpu *vcpu)
    > static inline unsigned long pending_irqs(struct kvm_vcpu *vcpu)
    > {
    > return pending_irqs_no_gisa(vcpu) |
    > - gisa_get_ipm(vcpu->kvm->arch.gisa) << IRQ_PEND_IO_ISC_7;
    > + gisa_get_ipm(vcpu->kvm->arch.gisa_int.origin) <<

    Unconditional call to gisa_get_ipm(), and get ipm just accesses ->ipm.

    > + IRQ_PEND_IO_ISC_7;
    > }
    >

    [..]

    > void kvm_s390_gisa_init(struct kvm *kvm)
    > {
    > + struct kvm_s390_gisa_interrupt *gi = &kvm->arch.gisa_int;
    > +
    > if (!css_general_characteristics.aiv)
    > return;
    > - kvm->arch.gisa = &kvm->arch.sie_page2->gisa;
    > + gi->origin = &kvm->arch.sie_page2->gisa;

    Should stay NULL if !css_general_characteristics.aiv.

    > kvm_s390_gisa_clear(kvm);
    > - VM_EVENT(kvm, 3, "gisa 0x%pK initialized", kvm->arch.gisa);
    > + VM_EVENT(kvm, 3, "gisa 0x%pK initialized", gi->origin);
    > }
    >

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