linux-kernel - [PATCH v2 27/52] irqchip/gic-v3-its: Support VPE doorbell invalidation even when !DirectLPI

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Date:   Wed, 28 Jun 2017 16:03:46 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu
Cc:     Christoffer Dall <christoffer.dall@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Eric Auger <eric.auger@...hat.com>,
        Shanker Donthineni <shankerd@...eaurora.org>,
        Mark Rutland <mark.rutland@....com>
Subject: [PATCH v2 27/52] irqchip/gic-v3-its: Support VPE doorbell invalidation even when !DirectLPI

When we don't have the DirectLPI feature, we must work around the
architecture shortcomings to be able to perform the required
invalidation.

For this, we create a fake device whose sole purpose is to
provide a way to issue a map/inv/unmap sequence (and the corresponding
sync operations). That's 6 commands and a full serialization point
to be able to do this.

You just have to hope the hypervisor won't do that too often...

Reviewed-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 drivers/irqchip/irq-gic-v3-its.c | 66 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 63 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 64893f0427f2..4979916cd3d7 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -138,6 +138,9 @@ struct its_device {
 	u32			device_id;
 };
 
+static struct its_device *vpe_proxy_dev;
+static DEFINE_RAW_SPINLOCK(vpe_proxy_dev_lock);
+
 static LIST_HEAD(its_nodes);
 static DEFINE_SPINLOCK(its_lock);
 static struct rdists *gic_rdists;
@@ -2074,6 +2077,14 @@ static int its_msi_prepare(struct irq_domain *domain, struct device *dev,
 	msi_info = msi_get_domain_info(domain);
 	its = msi_info->data;
 
+	if (its->is_v4 && !gic_rdists->has_direct_lpi &&
+	    dev_id == vpe_proxy_dev->device_id) {
+		/* Bad luck. Get yourself a better implementation */
+		WARN_ONCE(1, "DevId %x clashes with GICv4 VPE proxy device\n",
+			  dev_id);
+		return -EINVAL;
+	}
+
 	its_dev = its_find_device(its, dev_id);
 	if (its_dev) {
 		/*
@@ -2318,10 +2329,38 @@ static int its_vpe_set_vcpu_affinity(struct irq_data *d, void *vcpu_info)
 static void its_vpe_send_inv(struct irq_data *d)
 {
 	struct its_vpe *vpe = irq_data_get_irq_chip_data(d);
-	void __iomem *rdbase;
 
-	rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
-	gic_write_invlpir(d->hwirq, rdbase + GICR_INVLPIR);
+	if (gic_rdists->has_direct_lpi) {
+		void __iomem *rdbase;
+
+		rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
+		gic_write_invlpir(d->hwirq, rdbase + GICR_INVLPIR);
+	} else {
+		/*
+		 * This is insane.
+		 *
+		 * If a GICv4 doesn't implement Direct LPIs, the only
+		 * way to perform an invalidate is to use a fake
+		 * device to issue a MAP/INV/UNMAP sequence. Since
+		 * each of these commands has a sync operation, this
+		 * is really fast. Not.
+		 *
+		 * We always use event 0, and thus serialize all VPE
+		 * invalidations in the system.
+		 *
+		 * Broken by design(tm).
+		 */
+		unsigned long flags;
+
+		raw_spin_lock_irqsave(&vpe_proxy_dev_lock, flags);
+
+		vpe_proxy_dev->event_map.col_map[0] = vpe->col_idx;
+		its_send_mapti(vpe_proxy_dev, vpe->vpe_db_lpi, 0);
+		its_send_inv(vpe_proxy_dev, 0);
+		its_send_discard(vpe_proxy_dev, 0);
+
+		raw_spin_unlock_irqrestore(&vpe_proxy_dev_lock, flags);
+	}
 }
 
 static void its_vpe_mask_irq(struct irq_data *d)
@@ -2616,6 +2655,27 @@ static int its_init_domain(struct fwnode_handle *handle, struct its_node *its)
 
 static int its_init_vpe_domain(void)
 {
+	struct its_node *its;
+	u32 devid;
+
+	if (gic_rdists->has_direct_lpi) {
+		pr_info("ITS: Using DirectLPI for VPE invalidation\n");
+		return 0;
+	}
+
+	/* Any ITS will do, even if not v4 */
+	its = list_first_entry(&its_nodes, struct its_node, entry);
+
+	/* Use the last possible DevID */
+	devid = GENMASK(its->device_ids - 1, 0);
+	vpe_proxy_dev = its_create_device(its, devid, 1);
+	if (!vpe_proxy_dev) {
+		pr_err("ITS: Can't allocate GICv4 proxy device\n");
+		return -ENODEV;
+	}
+
+	pr_info("ITS: Allocated DevID %x as GICv4 proxy device\n", devid);
+
 	return 0;
 }
 
-- 
2.11.0