On ARM64 platforms with GICv3 ITS, VFIO PCI passthrough currently cannot dynamically allocate MSI-X vectors after MSI-X has been enabled. When QEMU needs to extend the vector range, it must disable MSI-X, free all interrupts, then re-enable with a larger allocation. This creates an interrupt loss window for already-active vectors. Consider HNS3 with RoCE: NIC and RDMA share one PCI device and ITS DeviceID, with MSI-X vectors partitioned as NIC (lower range) then RoCE (starting at base_vector = num_nic_msi). In VFIO passthrough, loading hns_roce after hns3 forces QEMU to tear down all interrupts before re-allocating the larger range. During this process, NIC interrupts may be lost. Testing confirmed that this occasionally occurs, causing the network port reset to fail. ITS_MSI_FLAGS_SUPPORTED lacks MSI_FLAG_PCI_MSIX_ALLOC_DYN, causing pci_msix_can_alloc_dyn() to return false. VFIO then sets has_dyn_msix=false and never clears VFIO_IRQ_INFO_NORESIZE for MSI-X, keeping the old "disable and reallocate" behavior. The essential prerequisite for enabling this flag is the fix to msi_prepare() call timing (commit 1396e89e09f0 ("genirq/msi: Move prepare() call to per-device allocation")): msi_prepare() is now called once at per-device domain creation with hwsize, so ITS creates an ITT with sufficient capacity for all MSI-X vectors. Without this fix, msi_prepare() was called per-allocation with semi-random nvec, maybe resulting in an ITT too small for dynamic vector addition. With this in place, dynamic MSI-X allocation works correctly: msi_domain_alloc_irq_at() uses populate_alloc_info() to copy the pre-prepared alloc_data without re-invoking msi_prepare(), so each new vector simply gets a LPI entry in the already-allocated ITT, without affecting existing vectors. Signed-off-by: Jinqian Yang <yangjinqian1@huawei.com> --- drivers/irqchip/irq-gic-its-msi-parent.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/irqchip/irq-gic-its-msi-parent.c b/drivers/irqchip/irq-gic-its-msi-parent.c index b9257103a999..b2b9d2068bb1 100644 --- a/drivers/irqchip/irq-gic-its-msi-parent.c +++ b/drivers/irqchip/irq-gic-its-msi-parent.c @@ -18,7 +18,8 @@ #define ITS_MSI_FLAGS_SUPPORTED (MSI_GENERIC_FLAGS_MASK | \ MSI_FLAG_PCI_MSIX | \ - MSI_FLAG_MULTI_PCI_MSI) + MSI_FLAG_MULTI_PCI_MSI | \ + MSI_FLAG_PCI_MSIX_ALLOC_DYN) static int its_translate_frame_address(struct fwnode_handle *msi_node, phys_addr_t *pa) { -- 2.33.0