Re: [PATCH] kvm: fix race with level interrupts

From: Gleb Natapov
Date: Thu Jul 19 2012 - 03:51:48 EST

On Thu, Jul 19, 2012 at 01:44:59AM +0300, Michael S. Tsirkin wrote:
> On Wed, Jul 18, 2012 at 04:16:14PM -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@xxxxxxxxxx>
> > > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > > ---
> > >
> > > 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)
> > > +{
> > > + /* 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)
> >
> > Please use "irq_source_id" and keep "level". I hate reviewing code
> > where I have to differentiate 'l' vs '1'.
>
> l is an illegal variable name? Switch to a different font.
>
No, but it does not make it good variable name. I agree with Alex here.

> > Same below, mixing src_id and
> > irq_source_id in various places.
>
> irq_source_id is too long, coding style says variable names
> should be short:
> LOCAL variable names should be short, and to the point.
Again I agree with Alex about consistency.

>
> > > {
> > > - struct kvm_pic *s = opaque;
> > > int ret = -1;
> > > + int level;
> >
> > And you'd avoid this variable
>
> by giving a different meaning to the same variable in
> different parts of a function? Now *that* is a bad idea.
>
> l is level for a specific source, level is the resulting irq value.
>
You can call it shared_level if you wish, but what's wrong with doing:
ret = pic_set_irq1(&s->pics[irq >> 3], irq & 7,
kvm_irq_line_state(&s->irq_states[irq], src_id, l));


> > >
> > > 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);
> > > }
> >
> >

--
Gleb.
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