linux-kernel - [PATCH v3 27/59] irqchip/gic-v3-its: Support VPE doorbell invalidation even when !DirectLPI

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Date:   Mon, 31 Jul 2017 18:26:05 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org
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>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>
Subject: [PATCH v3 27/59] 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 | 73 ++++++++++++++++++++++++++++++++++++++--
 1 file changed, 70 insertions(+), 3 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index d871d105be9d..210840e0ec92 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -136,6 +136,9 @@ 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;
@@ -2077,6 +2080,14 @@ 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) {
 		/*
@@ -2330,13 +2341,48 @@ static int its_vpe_set_vcpu_affinity(struct irq_data *d, void *vcpu_info)
 	}
 }
 
+static void its_vpe_send_cmd(struct its_vpe *vpe,
+			     void (*cmd)(struct its_device *, u32))
+{
+	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);
+	cmd(vpe_proxy_dev, 0);
+	its_send_discard(vpe_proxy_dev, 0);
+
+	raw_spin_unlock_irqrestore(&vpe_proxy_dev_lock, flags);
+}
+
 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_lpir(vpe->vpe_db_lpi, 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_lpir(vpe->vpe_db_lpi, rdbase + GICR_INVLPIR);
+	} else {
+		/*
+		 * This is insane.
+		 *
+		 * If a GICv4 doesn't implement Direct LPIs (which is
+		 * extremely likely), 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).
+		 */
+		its_vpe_send_cmd(vpe, its_send_inv);
+	}
 }
 
 static void its_vpe_mask_irq(struct irq_data *d)
@@ -2638,6 +2684,27 @@ 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