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Date: Wed, 18 Jul 2012 16:26:41 -0600
From: Alex Williamson <alex.williamson@...hat.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
gleb@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kvm: fix race with level interrupts
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@...hat.com>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.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.
> +{
> + /* 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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