kern/60247: virtio(4): legacy attach fails when BAR0 is MMIO

["petri.koistinen%iki.fi@localhost via gnats" <gnats-admin%NetBSD.org@localhost>]

>Number:         60247
>Category:       kern
>Synopsis:       virtio(4): legacy attach fails when BAR0 is MMIO
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon May 11 00:40:00 +0000 2026
>Originator:     Petri Koistinen
>Release:        NetBSD 10.1 (virtio_pci.c rev 1.38.4.6); also rev 1.55 in -current
>Organization:
>Environment:
Host: macOS 26.4.1 on Apple Silicon
Hypervisor: Parallels Desktop 26.3.0
Guest: NetBSD 10.1 evbarm/aarch64
Guest NIC: virtio adapter
>Description:
virtio_pci_attach_09() hardcodes PCI_MAPREG_TYPE_IO when mapping
BAR0. Attach therefore fails on hosts that present BAR0 as
memory. Parallels does this for its legacy virtio NIC: the
driver reports "can't map i/o space" and the guest boots with
no NIC.

Legacy virtio is normally an I/O BAR interface, so the MMIO
BAR0 is not strictly spec-compliant. This is an
interoperability fix: use the BAR type PCI advertises instead
of forcing PCI_MAPREG_TYPE_IO. The modern (1.0) attach path
already does this.
>How-To-Repeat:
Boot NetBSD 10.1 evbarm/aarch64 GENERIC64 in Parallels Desktop
on Apple Silicon with the virtio NIC. dmesg contains:

virtio0 at pci0 dev 5 function 0
virtio0: can't map i/o space

and ifconfig -a shows only lo0.
>Fix:
--- src/sys/dev/pci/virtio_pci.c	(revision 1.55)
+++ src/sys/dev/pci/virtio_pci.c	(patched)
@@ -395,11 +395,14 @@
 	struct virtio_pci_softc * const psc = device_private(self);
 	const struct pci_attach_args * const pa = aux;
 	struct virtio_softc * const sc = &psc->sc_sc;
+	pcireg_t bar_type;

-	/* complete IO region */
-	if (pci_mapreg_map(pa, PCI_MAPREG_START, PCI_MAPREG_TYPE_IO, 0,
+	/* complete BAR0 region */
+	bar_type = pci_mapreg_type(pa->pa_pc, pa->pa_tag, PCI_MAPREG_START);
+	if (pci_mapreg_map(pa, PCI_MAPREG_START, bar_type, 0,
 		&psc->sc_iot, &psc->sc_ioh, NULL, &psc->sc_iosize)) {
-		aprint_error_dev(self, "can't map i/o space\n");
+		aprint_error_dev(self, "can't map BAR0 (%s)\n",
+			bar_type == PCI_MAPREG_TYPE_IO ? "I/O" : "MEM");
 		return EIO;
 	}

Tested: GENERIC64 cross-built from netbsd-10.1 source with this
patch boots and attaches vioif0.