irqchip/gic-v2m: Handle Multiple MSI base IRQ Alignment

The PCI Local Bus Specification 3.0 (section 6.8.1.6) allows modifying the
low-order bits of the MSI Message DATA register to encode nr_irqs interrupt
numbers in the log2(nr_irqs) bits for the domain.

The problem arises if the base vector (GICV2m base spi) is not aligned with
nr_irqs; in this case, the low-order log2(nr_irqs) bits from the base
vector conflict with the nr_irqs masking, causing the wrong MSI interrupt
to be identified.

To fix this, use bitmap_find_next_zero_area_off() instead of
bitmap_find_free_region() to align the initial base vector with nr_irqs.

Signed-off-by: Christian Bruel <christian.bruel@foss.st.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/all/20250902091045.220847-1-christian.bruel@foss.st.com

diff --git a/drivers/irqchip/irq-gic-v2m.c b/drivers/irqchip/irq-gic-v2m.c
index 24ef5af569fe4eb68e77dcfd5eabb5a07149a99c..8a3410c2b7b575ce1ff908e5fca3802770da8b36 100644 (file)
--- a/drivers/irqchip/irq-gic-v2m.c
+++ b/drivers/irqchip/irq-gic-v2m.c
@@ -153,14 +153,19 @@ static int gicv2m_irq_domain_alloc(struct irq_domain *domain, unsigned int virq,
 {
        msi_alloc_info_t *info = args;
        struct v2m_data *v2m = NULL, *tmp;
-       int hwirq, offset, i, err = 0;
+       int hwirq, i, err = 0;
+       unsigned long offset;
+       unsigned long align_mask = nr_irqs - 1;
 
        spin_lock(&v2m_lock);
        list_for_each_entry(tmp, &v2m_nodes, entry) {
-               offset = bitmap_find_free_region(tmp->bm, tmp->nr_spis,
-                                                get_count_order(nr_irqs));
-               if (offset >= 0) {
+               unsigned long align_off = tmp->spi_start - (tmp->spi_start & ~align_mask);
+
+               offset = bitmap_find_next_zero_area_off(tmp->bm, tmp->nr_spis, 0,
+                                                       nr_irqs, align_mask, align_off);
+               if (offset < tmp->nr_spis) {
                        v2m = tmp;
+                       bitmap_set(v2m->bm, offset, nr_irqs);
                        break;
                }
        }