linux-kernel - [RFC PATCH 28/33] irqchip/gic-v3-its: Support VPE doorbell invalidation even when !DirectLPI

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Date:   Tue, 17 Jan 2017 10:20:49 +0000
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>
Subject: [RFC PATCH 28/33] 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 hope the hypervisor won't do that too often...

Signed-off-by: Marc Zyngier <marc.zyngier@....com>
---
 drivers/irqchip/irq-gic-v3-its.c | 59 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 57 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 008fb71..3787579 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -133,6 +133,9 @@ 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;
@@ -993,8 +996,35 @@ static void lpi_update_config(struct irq_data *d, u8 clr, u8 set)
 		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;
-		writeq_relaxed(d->hwirq, rdbase + GICR_INVLPIR);
+		if (gic_rdists->has_direct_lpi) {
+			rdbase = per_cpu_ptr(gic_rdists->rdist, vpe->col_idx)->rd_base;
+			writeq_relaxed(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 this 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_mapvi(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);
+		}
 	}
 }
 
@@ -2481,6 +2511,31 @@ static struct irq_domain *its_init_vpe_domain(void)
 	struct fwnode_handle *handle;
 	struct irq_domain *domain;
 
+	if (gic_rdists->has_direct_lpi) {
+		pr_info("ITS: Using DirectLPI for VPE invalidation\n");
+	} else {
+		struct its_node *its;
+
+		list_for_each_entry(its, &its_nodes, entry) {
+			u32 devid;
+
+			if (!its->is_v4)
+				continue;
+
+			/* 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 NULL;
+			}
+
+			pr_info("ITS: Allocated DevID %x as GICv4 proxy device\n",
+				devid);
+			break;
+		}
+	}
+
 	handle = irq_domain_alloc_fwnode("VPE domain");
 	if (!handle)
 		return NULL;
-- 
2.1.4