On Fri, Oct 02, 2015 at 03:52:42PM +0100, Andre Przywara wrote:
> Hi Christoffer,
>
> On 29/09/15 15:49, Christoffer Dall wrote:
> > Currently vgic_process_maintenance() processes dealing with a completed
> > level-triggered interrupt directly, but we are soon going to reuse this
> > logic for level-triggered mapped interrupts with the HW bit set, so
> > move this logic into a separate static function.
> >
> > Probably the most scary part of this commit is convincing yourself that
> > the current flow is safe compared to the old one. In the following I
> > try to list the changes and why they are harmless:
> >
> > Move vgic_irq_clear_queued after kvm_notify_acked_irq:
> > Harmless because the only potential effect of clearing the queued
> > flag wrt. kvm_set_irq is that vgic_update_irq_pending does not set
> > the pending bit on the emulated CPU interface or in the
> > pending_on_cpu bitmask if the function is called with level=1.
> > However, the point of kvm_notify_acked_irq is to call kvm_set_irq
> > with level=0, and we set the queued flag again in
> > __kvm_vgic_sync_hwstate later on if the level is stil high.
> >
> > Move vgic_set_lr before kvm_notify_acked_irq:
> > Also, harmless because the LR are cpu-local operations and
> > kvm_notify_acked only affects the dist
> >
> > Move vgic_dist_irq_clear_soft_pend after kvm_notify_acked_irq:
> > Also harmless because it's just a bit which is cleared and altering
> > the line state does not affect this bit.
>
> Mmmh, kvm_set_irq(level=0) will eventually execute (in
> vgic_update_irq_pending()):
>
> vgic_dist_irq_clear_level(vcpu, irq_num);
> if (!vgic_dist_irq_soft_pend(vcpu, irq_num))
> vgic_dist_irq_clear_pending(vcpu, irq_num);
>
> So with the former code we would clear the (dist) pending bit if
> soft_pend was set before, while with the newer code we wouldn't.
> Is this just still working because Linux guests will never set the
> soft_pend bit? Or is this safe because will always clear the pending bit
> anyway later on? (my brain is too much jellyfish by now to still work
> this dependency out)
> Or what do I miss here?
>
you're right, I need to add a check for the level state and clear the
pnding bit in the vgic_dist_irq_clear_soft_pend() function as well.
> >
> > Reviewed-by: Eric Auger <eric.auger@xxxxxxxxxx>
> > Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> > Signed-off-by: Christoffer Dall <christoffer.dall@xxxxxxxxxx>
> > ---
> > virt/kvm/arm/vgic.c | 88 ++++++++++++++++++++++++++++++-----------------------
> > 1 file changed, 50 insertions(+), 38 deletions(-)
> >
> > diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> > index 6bd1c9b..fe0e5db 100644
> > --- a/virt/kvm/arm/vgic.c
> > +++ b/virt/kvm/arm/vgic.c
> > @@ -1322,12 +1322,56 @@ epilog:
> > }
> > }
> >
> > +static int process_level_irq(struct kvm_vcpu *vcpu, int lr, struct vgic_lr vlr)
> > +{
> > + int level_pending = 0;
>
> Why is this an int and not a bool? Also see below ...
>
because I apply a bitwise or operation in the caller, and I wasn't sure
if this was strictly kosher to do that on a bool, so I Googled it, and
found some reports of that going wrong on certain compilers, so I
figured better safe than sorry.
I couldn't easily dig up that resource again though.
> > +
> > + vlr.state = 0;
> > + vlr.hwirq = 0;
> > + vgic_set_lr(vcpu, lr, vlr);
> > +
> > + /*
> > + * If the IRQ was EOIed (called from vgic_process_maintenance) or it
> > + * went from active to non-active (called from vgic_sync_hwirq) it was
> > + * also ACKed and we we therefore assume we can clear the soft pending
> > + * state (should it had been set) for this interrupt.
> > + *
> > + * Note: if the IRQ soft pending state was set after the IRQ was
> > + * acked, it actually shouldn't be cleared, but we have no way of
> > + * knowing that unless we start trapping ACKs when the soft-pending
> > + * state is set.
> > + */
> > + vgic_dist_irq_clear_soft_pend(vcpu, vlr.irq);
> > +
> > + /*
> > + * Tell the gic to start sampling the line of this interrupt again.
> > + */
> > + vgic_irq_clear_queued(vcpu, vlr.irq);
> > +
> > + /* Any additional pending interrupt? */
> > + if (vgic_dist_irq_get_level(vcpu, vlr.irq)) {
> > + vgic_cpu_irq_set(vcpu, vlr.irq);
> > + level_pending = 1;
> > + } else {
> > + vgic_dist_irq_clear_pending(vcpu, vlr.irq);
> > + vgic_cpu_irq_clear(vcpu, vlr.irq);
> > + }
> > +
> > + /*
> > + * Despite being EOIed, the LR may not have
> > + * been marked as empty.
> > + */
> > + vgic_sync_lr_elrsr(vcpu, lr, vlr);
> > +
> > + return level_pending;
> > +}
> > +
> > static bool vgic_process_maintenance(struct kvm_vcpu *vcpu)
> > {
> > u32 status = vgic_get_interrupt_status(vcpu);
> > struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> > - bool level_pending = false;
> > struct kvm *kvm = vcpu->kvm;
> > + int level_pending = 0;
>
> Why this change here? Even after 8/8 I don't see any use of values
> outside of true/false.
>
See above.
Thanks for the review,
-Christoffer
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