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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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