[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH 2/4] xen/arm: do not use is_running to decide whether we can write directly to the LR registers
On Fri, 15 Feb 2013, Stefano Stabellini wrote: > During context switch is_running is set for the next vcpu before the > gic state is actually saved. > This leads to possible nasty races when interrupts need to be injected > after is_running is set to the next vcpu but before the currently > running gic state has been saved from the previous vcpu. > Introduce a new gic_running internal variable to precisely determine > which one is the vcpu currently using the gic. > > Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx> Although the description of the problem is accurate, the fix doesn't take SMP into consideration. Probably gic_running needs to be a per_cpu variable. In any case, I'll rework and resent the patch. > xen/arch/arm/gic.c | 8 +++++++- > 1 files changed, 7 insertions(+), 1 deletions(-) > > diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c > index 0ecc0f1..88f2d3a 100644 > --- a/xen/arch/arm/gic.c > +++ b/xen/arch/arm/gic.c > @@ -53,6 +53,7 @@ static irq_desc_t irq_desc[NR_IRQS]; > static DEFINE_PER_CPU(irq_desc_t[NR_LOCAL_IRQS], local_irq_desc); > static DEFINE_PER_CPU(uint64_t, lr_mask); > static gic_callback_fn_t gic_callbacks[NR_IRQS]; > +static struct vcpu *gic_running; > > unsigned nr_lrs; > > @@ -70,6 +71,7 @@ void gic_save_state(struct vcpu *v) > for ( i=0; i<nr_lrs; i++) > v->arch.gic_lr[i] = GICH[GICH_LR + i]; > v->arch.lr_mask = this_cpu(lr_mask); > + gic_running = NULL; > spin_unlock_irq(&gic.lock); > /* Disable until next VCPU scheduled */ > GICH[GICH_HCR] = 0; > @@ -81,12 +83,16 @@ void gic_restore_state(struct vcpu *v) > int i; > > if ( is_idle_vcpu(v) ) > + { > + gic_running = v; > return; > + } > > spin_lock_irq(&gic.lock); > this_cpu(lr_mask) = v->arch.lr_mask; > for ( i=0; i<nr_lrs; i++) > GICH[GICH_LR + i] = v->arch.gic_lr[i]; > + gic_running = v; > spin_unlock_irq(&gic.lock); > GICH[GICH_HCR] = GICH_HCR_EN; > isb(); > @@ -481,7 +487,7 @@ void gic_set_guest_irq(struct vcpu *v, unsigned int > virtual_irq, > > spin_lock_irqsave(&gic.lock, flags); > > - if ( v->is_running && list_empty(&v->arch.vgic.lr_pending) ) > + if ( v == gic_running && list_empty(&v->arch.vgic.lr_pending) ) > { > i = find_first_zero_bit(&this_cpu(lr_mask), nr_lrs); > if (i < nr_lrs) { > -- > 1.7.2.5 > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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