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    SubjectRe: [PATCH] kvm: fix race with level interrupts
    On Wed, Jul 18, 2012 at 04:26:41PM -0600, Alex Williamson wrote:
    > On Thu, 2012-07-19 at 00:52 +0300, Michael S. Tsirkin wrote:
    > > When more than 1 source id is in use for the same GSI, we have the
    > > following race related to handling irq_states:
    > >
    > > CPU 0 clears bit in irq_states. CPU 0 reads irq_state as 0.
    > > CPU 1 sets bit in irq_states. CPU 1 calls kvm_ioapic_set_irq(1). CPU 0
    > > calls kvm_ioapic_set_irq(0).
    > >
    > > Now ioapic thinks the level is 0 but irq_state is not 0.
    > >
    > > Note that above is valid behaviour if CPU0 and CPU1 are using different
    > > source ids.
    > >
    > > Fix by performing all irq_states bitmap handling under pic/ioapic lock.
    > > This also removes the need for atomics with irq_states handling.
    > >
    > > Reported-by: Gleb Natapov <gleb@redhat.com>
    > > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
    > > ---
    > >
    > > This survives stress testing for me (though I only tried virtio, not
    > > device assignment).
    > > Avi, Marcelo, though we have not observed this in the field,
    > > it's a bugfix so probably 3.5 material?
    > > I assume yes so the patch is against 3.5-rc7.
    > > Also stable? It's a very old bug.
    > >
    > >
    > > arch/x86/include/asm/kvm_host.h | 15 ++++++++++++++-
    > > arch/x86/kvm/i8259.c | 14 ++++++++++++--
    > > virt/kvm/ioapic.c | 13 ++++++++++++-
    > > virt/kvm/ioapic.h | 4 +++-
    > > virt/kvm/irq_comm.c | 31 ++++---------------------------
    > > 5 files changed, 45 insertions(+), 32 deletions(-)
    > >
    > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
    > > index db7c1f2..fe6e9f1 100644
    > > --- a/arch/x86/include/asm/kvm_host.h
    > > +++ b/arch/x86/include/asm/kvm_host.h
    > > @@ -802,7 +802,20 @@ int kvm_read_guest_page_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
    > > void kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
    > > bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl);
    > >
    > > -int kvm_pic_set_irq(void *opaque, int irq, int level);
    > > +static inline int kvm_irq_line_state(unsigned long *irq_state,
    > > + int irq_source_id, int level)
    >
    > This should probably be __kvm_irq_line_state given the calling
    > restrictions.

    It's such a trivial helper, do we need to split hairs about this?

    Look it's not a good time for minor coding style nits.
    3.5 is imminent, it's about 1am here and I really don't have time to retest
    today, so we'll release another kernel with a bug.

    Could you focus on reviewing the functionality and correctness, and
    leave ideas for better variable naming aside until 3.6?

    > > +{
    > > + /* Logical OR for level trig interrupt */
    > > + if (level)
    > > + __set_bit(irq_source_id, irq_state);
    > > + else
    > > + __clear_bit(irq_source_id, irq_state);
    > > +
    > > + return !!(*irq_state);
    > > +}
    > > +
    > > +int kvm_pic_set_irq(struct kvm_pic *pic, int irq, int irq_source_id, int level);
    > > +void kvm_pic_clear_all(struct kvm_pic *pic, int irq_source_id);
    > >
    > > void kvm_inject_nmi(struct kvm_vcpu *vcpu);
    > >
    > > diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
    > > index 81cf4fa..95b504b 100644
    > > --- a/arch/x86/kvm/i8259.c
    > > +++ b/arch/x86/kvm/i8259.c
    > > @@ -188,13 +188,14 @@ void kvm_pic_update_irq(struct kvm_pic *s)
    > > pic_unlock(s);
    > > }
    > >
    > > -int kvm_pic_set_irq(void *opaque, int irq, int level)
    > > +int kvm_pic_set_irq(struct kvm_pic *s, int irq, int src_id, int l)
    > > {
    > > - struct kvm_pic *s = opaque;
    > > int ret = -1;
    > > + int level;
    > >
    > > pic_lock(s);
    > > if (irq >= 0 && irq < PIC_NUM_PINS) {
    > > + level = kvm_irq_line_state(&s->irq_states[irq], src_id, l);
    > > ret = pic_set_irq1(&s->pics[irq >> 3], irq & 7, level);
    > > pic_update_irq(s);
    > > trace_kvm_pic_set_irq(irq >> 3, irq & 7, s->pics[irq >> 3].elcr,
    > > @@ -205,6 +206,15 @@ int kvm_pic_set_irq(void *opaque, int irq, int level)
    > > return ret;
    > > }
    > >
    > > +void kvm_pic_clear_all(struct kvm_pic *s, int src_id)
    > > +{
    > > + int i;
    > > + pic_lock(s);
    > > + for (i = 0; i < PIC_NUM_PINS; i++)
    > > + __clear_bit(src_id, &s->irq_states[i]);
    > > + pic_unlock(s);
    > > +}
    > > +
    > > /*
    > > * acknowledge interrupt 'irq'
    > > */
    > > diff --git a/virt/kvm/ioapic.c b/virt/kvm/ioapic.c
    > > index 26fd54d..268b332 100644
    > > --- a/virt/kvm/ioapic.c
    > > +++ b/virt/kvm/ioapic.c
    > > @@ -191,17 +191,19 @@ static int ioapic_deliver(struct kvm_ioapic *ioapic, int irq)
    > > return kvm_irq_delivery_to_apic(ioapic->kvm, NULL, &irqe);
    > > }
    > >
    > > -int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level)
    > > +int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int src_id, int l)
    > > {
    > > u32 old_irr;
    > > u32 mask = 1 << irq;
    > > union kvm_ioapic_redirect_entry entry;
    > > int ret = 1;
    > > + int level;
    > >
    > > spin_lock(&ioapic->lock);
    > > old_irr = ioapic->irr;
    > > if (irq >= 0 && irq < IOAPIC_NUM_PINS) {
    > > entry = ioapic->redirtbl[irq];
    > > + level = kvm_irq_line_state(&ioapic->irq_states[irq], src_id, l);
    > > level ^= entry.fields.polarity;
    > > if (!level)
    > > ioapic->irr &= ~mask;
    > > @@ -221,6 +223,15 @@ int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level)
    > > return ret;
    > > }
    > >
    > > +void kvm_ioapic_clear_all(struct kvm_ioapic *ioapic, int src_id)
    > > +{
    > > + int i;
    > > + spin_lock(&ioapic->lock);
    > > + for (i = 0; i < KVM_IOAPIC_NUM_PINS; i++)
    > > + __clear_bit(src_id, &ioapic->irq_states[i]);
    > > + spin_unlock(&ioapic->lock);
    > > +}
    > > +
    > > static void __kvm_ioapic_update_eoi(struct kvm_ioapic *ioapic, int vector,
    > > int trigger_mode)
    > > {
    > > diff --git a/virt/kvm/ioapic.h b/virt/kvm/ioapic.h
    > > index 32872a0..a30abfe 100644
    > > --- a/virt/kvm/ioapic.h
    > > +++ b/virt/kvm/ioapic.h
    > > @@ -74,7 +74,9 @@ void kvm_ioapic_update_eoi(struct kvm *kvm, int vector, int trigger_mode);
    > > bool kvm_ioapic_handles_vector(struct kvm *kvm, int vector);
    > > int kvm_ioapic_init(struct kvm *kvm);
    > > void kvm_ioapic_destroy(struct kvm *kvm);
    > > -int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int level);
    > > +int kvm_ioapic_set_irq(struct kvm_ioapic *ioapic, int irq, int irq_source_id,
    > > + int level);
    > > +void kvm_ioapic_clear_all(struct kvm_ioapic *ioapic, int irq_source_id);
    > > void kvm_ioapic_reset(struct kvm_ioapic *ioapic);
    > > int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
    > > struct kvm_lapic_irq *irq);
    > > diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
    > > index 5afb431..83402d7 100644
    > > --- a/virt/kvm/irq_comm.c
    > > +++ b/virt/kvm/irq_comm.c
    > > @@ -33,26 +33,12 @@
    > >
    > > #include "ioapic.h"
    > >
    > > -static inline int kvm_irq_line_state(unsigned long *irq_state,
    > > - int irq_source_id, int level)
    > > -{
    > > - /* Logical OR for level trig interrupt */
    > > - if (level)
    > > - set_bit(irq_source_id, irq_state);
    > > - else
    > > - clear_bit(irq_source_id, irq_state);
    > > -
    > > - return !!(*irq_state);
    > > -}
    > > -
    > > static int kvm_set_pic_irq(struct kvm_kernel_irq_routing_entry *e,
    > > struct kvm *kvm, int irq_source_id, int level)
    > > {
    > > #ifdef CONFIG_X86
    > > struct kvm_pic *pic = pic_irqchip(kvm);
    > > - level = kvm_irq_line_state(&pic->irq_states[e->irqchip.pin],
    > > - irq_source_id, level);
    > > - return kvm_pic_set_irq(pic, e->irqchip.pin, level);
    > > + return kvm_pic_set_irq(pic, e->irqchip.pin, irq_source_id, level);
    > > #else
    > > return -1;
    > > #endif
    > > @@ -62,10 +48,7 @@ static int kvm_set_ioapic_irq(struct kvm_kernel_irq_routing_entry *e,
    > > struct kvm *kvm, int irq_source_id, int level)
    > > {
    > > struct kvm_ioapic *ioapic = kvm->arch.vioapic;
    > > - level = kvm_irq_line_state(&ioapic->irq_states[e->irqchip.pin],
    > > - irq_source_id, level);
    > > -
    > > - return kvm_ioapic_set_irq(ioapic, e->irqchip.pin, level);
    > > + return kvm_ioapic_set_irq(ioapic, e->irqchip.pin, irq_source_id, level);
    > > }
    > >
    > > inline static bool kvm_is_dm_lowest_prio(struct kvm_lapic_irq *irq)
    > > @@ -249,8 +232,6 @@ unlock:
    > >
    > > void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id)
    > > {
    > > - int i;
    > > -
    > > ASSERT(irq_source_id != KVM_USERSPACE_IRQ_SOURCE_ID);
    > >
    > > mutex_lock(&kvm->irq_lock);
    > > @@ -263,14 +244,10 @@ void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id)
    > > if (!irqchip_in_kernel(kvm))
    > > goto unlock;
    > >
    > > - for (i = 0; i < KVM_IOAPIC_NUM_PINS; i++) {
    > > - clear_bit(irq_source_id, &kvm->arch.vioapic->irq_states[i]);
    > > - if (i >= 16)
    > > - continue;
    > > + kvm_ioapic_clear_all(kvm->arch.vioapic, irq_source_id);
    > > #ifdef CONFIG_X86
    > > - clear_bit(irq_source_id, &pic_irqchip(kvm)->irq_states[i]);
    > > + kvm_pic_clear_all(pic_irqchip(kvm), irq_source_id);
    > > #endif
    > > - }
    > > unlock:
    > > mutex_unlock(&kvm->irq_lock);
    > > }
    >
    >


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