[tip: irq/urgent] irqchip/gic-v4: Correctly deal with set_affinity on lazily-mapped VPEs

[tip-bot2 for Marc Zyngier]

The following commit has been merged into the irq/urgent branch of tip:

Commit-ID:     e6c24e2d05bb05de96ffb9bdb0ee62d20ad526f8
Gitweb:        https://git.kernel.org/tip/e6c24e2d05bb05de96ffb9bdb0ee62d20ad526f8
Author:        Marc Zyngier <maz@xxxxxxxxxx>
AuthorDate:    Sun, 27 Oct 2024 10:22:20 
Committer:     Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitterDate: Sun, 27 Oct 2024 17:30:16 +01:00

irqchip/gic-v4: Correctly deal with set_affinity on lazily-mapped VPEs

Zenghui points out that a recent change to the way set_affinity is
handled for VPEs has the potential to return an error if the VPE
hasn't been mapped yet (because the guest hasn't emited a MAPTI
command yet), affecting GICv4.0 implementations that rely on the
ITSList feature.

Fix this by making the set_affinity succeed in this case, and
return early, without trying to touch the HW.

Fixes: 1442ee0011983 ("irqchip/gic-v4: Don't allow a VMOVP on a dying VPE")
Reported-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Reviewed-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
Link: https://lore.kernel.org/all/20241027102220.1858558-1-maz@xxxxxxxxxx
Link: https://lore.kernel.org/r/aab45cd3-e5ca-58cf-e081-e32a17f5b4e7@xxxxxxxxxx

---
 drivers/irqchip/irq-gic-v3-its.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index ab597e7..52f625e 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -3810,8 +3810,18 @@ static int its_vpe_set_affinity(struct irq_data *d,
 	 * Check if we're racing against a VPE being destroyed, for
 	 * which we don't want to allow a VMOVP.
 	 */
-	if (!atomic_read(&vpe->vmapp_count))
-		return -EINVAL;
+	if (!atomic_read(&vpe->vmapp_count)) {
+		if (gic_requires_eager_mapping())
+			return -EINVAL;
+
+		/*
+		 * If we lazily map the VPEs, this isn't an error and
+		 * we can exit cleanly.
+		 */
+		cpu = cpumask_first(mask_val);
+		irq_data_update_effective_affinity(d, cpumask_of(cpu));
+		return IRQ_SET_MASK_OK_DONE;
+	}
 
 	/*
 	 * Changing affinity is mega expensive, so let's be as lazy as