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Wed, 07 Apr 2021 15:51:15 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 7CF64B17A; Wed, 7 Apr 2021 15:51:14 +0000 (UTC) X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" X-Inumbo-ID: cb1f6193-4909-446a-b680-92eb6c454dee X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1617810674; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=36g4tBJYkFl96eornkmZi6TegJJU/GrB2pStwKTEVeg=; b=oyO1VPv9PqNGf7TeXYArMHt00GP2UUK+w3gKKIVir3ytaDDlsmq3TfGpzryb4r6W5eKIOg coQ24OdTbziB8mNw4bspNGUhEjNjEY4A9r041r/AdxRYHYdIj2dO0o8EGnYUgpCUowA0y/ /twISYtMvHQ3xHKncxMVeCEJ5uOkbPQ= Subject: Re: [PATCH v3 06/11] x86/hvm: allowing registering EOI callbacks for GSIs To: Roger Pau Monne Cc: Andrew Cooper , Wei Liu , xen-devel@lists.xenproject.org References: <20210331103303.79705-1-roger.pau@citrix.com> <20210331103303.79705-7-roger.pau@citrix.com> From: Jan Beulich Message-ID: Date: Wed, 7 Apr 2021 17:51:14 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210331103303.79705-7-roger.pau@citrix.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit 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