From: Jan Beulich <jbeulich@suse.com>
To: Roger Pau Monne <roger.pau@citrix.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>, Wei Liu <wl@xen.org>,
xen-devel@lists.xenproject.org
Subject: Re: [PATCH v3 06/11] x86/hvm: allowing registering EOI callbacks for GSIs
Date: Wed, 7 Apr 2021 17:51:14 +0200 [thread overview]
Message-ID: <a57f0f75-341d-e6e1-823c-2083184a8f08@suse.com> (raw)
In-Reply-To: <20210331103303.79705-7-roger.pau@citrix.com>
On 31.03.2021 12:32, Roger Pau Monne wrote:
> --- a/xen/arch/x86/hvm/irq.c
> +++ b/xen/arch/x86/hvm/irq.c
> @@ -595,6 +595,69 @@ int hvm_local_events_need_delivery(struct vcpu *v)
> return !hvm_interrupt_blocked(v, intack);
> }
>
> +int hvm_gsi_register_callback(struct domain *d, unsigned int gsi,
> + struct hvm_gsi_eoi_callback *cb)
> +{
> + struct hvm_irq *hvm_irq = hvm_domain_irq(d);
> +
> + if ( gsi >= hvm_irq->nr_gsis )
> + {
> + ASSERT_UNREACHABLE();
> + return -EINVAL;
> + }
> +
> + write_lock(&hvm_irq->gsi_callbacks_lock);
> + list_add(&cb->list, &hvm_irq->gsi_callbacks[gsi]);
> + write_unlock(&hvm_irq->gsi_callbacks_lock);
> +
> + return 0;
> +}
> +
> +void hvm_gsi_unregister_callback(struct domain *d, unsigned int gsi,
> + struct hvm_gsi_eoi_callback *cb)
> +{
> + struct hvm_irq *hvm_irq = hvm_domain_irq(d);
> + const struct list_head *tmp;
> +
> + if ( gsi >= hvm_irq->nr_gsis )
> + {
> + ASSERT_UNREACHABLE();
> + return;
> + }
> +
> + write_lock(&hvm_irq->gsi_callbacks_lock);
> + list_for_each ( tmp, &hvm_irq->gsi_callbacks[gsi] )
> + if ( tmp == &cb->list )
> + {
> + list_del(&cb->list);
> + break;
> + }
> + write_unlock(&hvm_irq->gsi_callbacks_lock);
> +}
Perhaps somehow flag, at least in debug builds, if the callback
wasn#t found?
> +void hvm_gsi_execute_callbacks(unsigned int gsi)
> +{
> + struct hvm_irq *hvm_irq = hvm_domain_irq(current->domain);
> + struct hvm_gsi_eoi_callback *cb;
> +
> + read_lock(&hvm_irq->gsi_callbacks_lock);
> + list_for_each_entry ( cb, &hvm_irq->gsi_callbacks[gsi], list )
> + cb->callback(gsi, cb->data);
> + read_unlock(&hvm_irq->gsi_callbacks_lock);
> +}
Just as an observation (for now at least) - holding the lock here
means the callbacks cannot re-register themselves.
> +bool hvm_gsi_has_callbacks(const struct domain *d, unsigned int gsi)
> +{
> + struct hvm_irq *hvm_irq = hvm_domain_irq(d);
> + bool has_callbacks;
> +
> + read_lock(&hvm_irq->gsi_callbacks_lock);
> + has_callbacks = !list_empty(&hvm_irq->gsi_callbacks[gsi]);
> + read_unlock(&hvm_irq->gsi_callbacks_lock);
> +
> + return has_callbacks;
> +}
What use is this function? Its result is stale by the time the
caller can look at it, as you've dropped the lock.
> @@ -421,13 +423,25 @@ static void eoi_callback(unsigned int vector, void *data)
> if ( is_iommu_enabled(d) )
> {
> spin_unlock(&d->arch.hvm.irq_lock);
> - hvm_dpci_eoi(vioapic->base_gsi + pin);
> + hvm_dpci_eoi(gsi);
> spin_lock(&d->arch.hvm.irq_lock);
> }
>
> + /*
> + * Callbacks don't expect to be executed with any lock held, so
> + * drop the lock that protects the vIO-APIC fields from changing.
> + *
> + * Note that the redirection entry itself cannot go away, so upon
> + * retaking the lock we only need to avoid making assumptions on
> + * redirection entry field values (ie: recheck the IRR field).
> + */
> + spin_unlock(&d->arch.hvm.irq_lock);
> + hvm_gsi_execute_callbacks(gsi);
> + spin_lock(&d->arch.hvm.irq_lock);
The two pairs of unlock / re-lock want folding, I think - there's
no point causing extra contention on the lock here.
> @@ -443,7 +457,8 @@ static void ioapic_inj_irq(
> struct vlapic *target,
> uint8_t vector,
> uint8_t trig_mode,
> - uint8_t delivery_mode)
> + uint8_t delivery_mode,
> + bool callback)
> {
> HVM_DBG_LOG(DBG_LEVEL_IOAPIC, "irq %d trig %d deliv %d",
> vector, trig_mode, delivery_mode);
> @@ -452,7 +467,7 @@ static void ioapic_inj_irq(
> (delivery_mode == dest_LowestPrio));
>
> vlapic_set_irq_callback(target, vector, trig_mode,
> - trig_mode ? eoi_callback : NULL, NULL);
> + callback ? eoi_callback : NULL, NULL);
I think you'd better use trig_mode || callback here and ...
> @@ -466,6 +481,7 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin)
> struct vlapic *target;
> struct vcpu *v;
> unsigned int irq = vioapic->base_gsi + pin;
> + bool callback = trig_mode || hvm_gsi_has_callbacks(d, irq);
>
> ASSERT(spin_is_locked(&d->arch.hvm.irq_lock));
>
> @@ -492,7 +508,8 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin)
> target = vlapic_lowest_prio(d, NULL, 0, dest, dest_mode);
> if ( target != NULL )
> {
> - ioapic_inj_irq(vioapic, target, vector, trig_mode, delivery_mode);
> + ioapic_inj_irq(vioapic, target, vector, trig_mode, delivery_mode,
> + callback);
... invoke hvm_gsi_has_callbacks() right here and ...
> @@ -507,7 +524,7 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin)
> for_each_vcpu ( d, v )
> if ( vlapic_match_dest(vcpu_vlapic(v), NULL, 0, dest, dest_mode) )
> ioapic_inj_irq(vioapic, vcpu_vlapic(v), vector, trig_mode,
> - delivery_mode);
> + delivery_mode, callback);
... here, avoiding to call the function when you don't need the
result.
Jan
next prev parent reply other threads:[~2021-04-07 15:51 UTC|newest]
Thread overview: 51+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 10:32 [PATCH v3 00/11] x86/intr: introduce EOI callbacks and fix vPT Roger Pau Monne
2021-03-31 10:32 ` [PATCH v3 01/11] x86/hvm: drop vcpu parameter from vlapic EOI callbacks Roger Pau Monne
2021-03-31 16:02 ` Jan Beulich
2021-03-31 16:24 ` Andrew Cooper
2021-04-01 9:12 ` Roger Pau Monné
2021-04-01 11:06 ` Jan Beulich
2021-04-07 7:41 ` Roger Pau Monné
2021-04-07 8:19 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 02/11] x86/hvm: drop domain parameter from vioapic/vpic " Roger Pau Monne
2021-03-31 16:04 ` Jan Beulich
2021-04-01 9:15 ` Roger Pau Monné
2021-04-01 9:28 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 03/11] x86/vlapic: introduce an EOI callback mechanism Roger Pau Monne
2021-03-31 11:47 ` Andrew Cooper
2021-03-31 12:50 ` Roger Pau Monné
2021-04-07 14:55 ` Jan Beulich
2021-04-07 16:27 ` Roger Pau Monné
2021-04-08 6:20 ` Jan Beulich
2021-04-08 9:12 ` Roger Pau Monné
2021-04-08 10:49 ` Jan Beulich
2021-04-08 10:56 ` Roger Pau Monné
2021-03-31 10:32 ` [PATCH v3 04/11] x86/vmsi: use the newly introduced EOI callbacks Roger Pau Monne
2021-04-07 14:59 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 05/11] x86/vioapic: switch to use the EOI callback mechanism Roger Pau Monne
2021-04-07 15:19 ` Jan Beulich
2021-04-07 16:46 ` Roger Pau Monné
2021-04-08 6:27 ` Jan Beulich
2021-04-08 8:59 ` Roger Pau Monné
2021-04-08 10:52 ` Jan Beulich
2021-03-31 10:32 ` [PATCH v3 06/11] x86/hvm: allowing registering EOI callbacks for GSIs Roger Pau Monne
2021-04-07 15:51 ` Jan Beulich [this message]
2021-04-07 17:08 ` Roger Pau Monné
2021-04-08 6:34 ` Jan Beulich
2021-04-15 16:04 ` Roger Pau Monné
2021-04-16 7:29 ` Jan Beulich
2021-04-19 8:31 ` Roger Pau Monné
2021-04-08 12:52 ` Roger Pau Monné
2021-04-08 14:31 ` Jan Beulich
2021-04-08 15:06 ` Roger Pau Monné
2021-03-31 10:32 ` [PATCH v3 07/11] x86/dpci: move code Roger Pau Monne
2021-03-31 10:33 ` [PATCH v3 08/11] x86/dpci: switch to use a GSI EOI callback Roger Pau Monne
2021-04-08 14:49 ` Jan Beulich
2021-04-08 15:23 ` Roger Pau Monné
2021-03-31 10:33 ` [PATCH v3 09/11] x86/vpt: switch interrupt injection model Roger Pau Monne
2021-04-14 10:28 ` Jan Beulich
2021-04-14 13:37 ` Roger Pau Monné
2021-04-14 14:05 ` Jan Beulich
2021-04-14 14:20 ` Roger Pau Monné
2021-03-31 10:33 ` [PATCH v3 10/11] x86/vpt: remove vPT timers per-vCPU lists Roger Pau Monne
2021-04-14 10:38 ` Jan Beulich
2021-03-31 10:33 ` [PATCH v3 11/11] x86/vpt: introduce a per-vPT lock Roger Pau Monne
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