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

Marc Zyngier
2017-07-31T17:26:33Z

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@linutronix.de>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.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