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Re: [Xen-devel] [RFC PATCH v2 12/22] ARM: vGIC: protect gic_update_one_lr() with pending_irq lock

Hi Andre,

On 21/07/17 21:00, Andre Przywara wrote:
When we return from a domain with the active bit set in an LR,
we update our pending_irq accordingly. This touches multiple status
bits, so requires the pending_irq lock.

The commit title says "protect gic_update_one_lr()" but here you only mention about one path. Please explain why the other are safe.

Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
 xen/arch/arm/gic.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index 9637682..84b282b 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -508,6 +508,7 @@ void gic_update_one_lr(struct vcpu *v, int i)

     if ( lr_val.state & GICH_LR_ACTIVE )
+        vgic_irq_lock(p, flags);

The function has an ASSERT to check the IRQs are disabled. So it is not necessary to save/restore flags.

         set_bit(GIC_IRQ_GUEST_ACTIVE, &p->status);
         if ( test_bit(GIC_IRQ_GUEST_ENABLED, &p->status) &&
              test_and_clear_bit(GIC_IRQ_GUEST_QUEUED, &p->status) )
@@ -521,6 +522,7 @@ void gic_update_one_lr(struct vcpu *v, int i)
                 gdprintk(XENLOG_WARNING, "unable to inject hw irq=%d into d%dv%d: 
already active in LR%d\n",
                          irq, v->domain->domain_id, v->vcpu_id, i);
+        vgic_irq_unlock(p, flags);
     else if ( lr_val.state & GICH_LR_PENDING )


Julien Grall

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