[RFC PATCH 1/1] selftests: vfio: Add mmap fault and device reset test

[Vipin Sharma <vipinsh@google.com>]

Add a selftest to verify VFIO PCI device reset on an mmapped and faulted
device. The test maps all available BARs on the device, faults them,
and triggers a device reset via the VFIO_DEVICE_RESET ioctl.

This exercise uncovers a circular locking dependency introduced in
commit f5b16b802174 ("PCI: Suspend iommu function prior to resetting a
device"), where pci_dev_reset_iommu_prepare() acquires group->mutex
under vfio's vdev->memory_lock.

Assisted-by: Jetski:gemini-3.1-pro
Signed-off-by: Vipin Sharma <vipinsh@google.com>
---
 tools/testing/selftests/vfio/Makefile         |  1 +
 .../selftests/vfio/vfio_pci_mmap_reset_test.c | 60 +++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 tools/testing/selftests/vfio/vfio_pci_mmap_reset_test.c

diff --git a/tools/testing/selftests/vfio/Makefile b/tools/testing/selftests/vfio/Makefile
index 2c32c48db509..17b3a2fe215c 100644
--- a/tools/testing/selftests/vfio/Makefile
+++ b/tools/testing/selftests/vfio/Makefile
@@ -13,6 +13,7 @@ TEST_GEN_PROGS += vfio_pci_device_test
 TEST_GEN_PROGS += vfio_pci_device_init_perf_test
 TEST_GEN_PROGS += vfio_pci_driver_test
 TEST_GEN_PROGS += vfio_pci_sriov_uapi_test
+TEST_GEN_PROGS += vfio_pci_mmap_reset_test
 
 TEST_FILES += scripts/cleanup.sh
 TEST_FILES += scripts/lib.sh
diff --git a/tools/testing/selftests/vfio/vfio_pci_mmap_reset_test.c b/tools/testing/selftests/vfio/vfio_pci_mmap_reset_test.c
new file mode 100644
index 000000000000..b004867905de
--- /dev/null
+++ b/tools/testing/selftests/vfio/vfio_pci_mmap_reset_test.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/pci_regs.h>
+#include <linux/vfio.h>
+
+#include <libvfio.h>
+
+#include "kselftest_harness.h"
+
+static const char *device_bdf;
+
+FIXTURE(vfio_pci_mmap_reset_test) {
+	struct iommu *iommu;
+	struct vfio_pci_device *device;
+};
+
+FIXTURE_SETUP(vfio_pci_mmap_reset_test)
+{
+	self->iommu = iommu_init(MODE_IOMMUFD);
+	self->device = vfio_pci_device_init(device_bdf, self->iommu);
+}
+
+FIXTURE_TEARDOWN(vfio_pci_mmap_reset_test)
+{
+	vfio_pci_device_cleanup(self->device);
+	iommu_cleanup(self->iommu);
+}
+
+TEST_F(vfio_pci_mmap_reset_test, mmap_fault_and_reset)
+{
+	volatile char dummy;
+	bool has_mmap = false;
+	int i;
+
+	if (!(self->device->info.flags & VFIO_DEVICE_FLAGS_RESET))
+		SKIP(return, "Device does not support reset\n");
+
+	for (i = 0; i < PCI_STD_NUM_BARS; i++) {
+		struct vfio_pci_bar *bar = &self->device->bars[i];
+
+		if (!bar->vaddr)
+			continue;
+
+		/* Touch BAR to trigger page fault under mmap_lock */
+		dummy = *(volatile char *)bar->vaddr;
+		(void)dummy;
+		has_mmap = true;
+	}
+
+	if (!has_mmap)
+		SKIP(return, "No mmapable BAR found on device\n");
+
+	/* Trigger device reset under memory_lock */
+	vfio_pci_device_reset(self->device);
+}
+
+int main(int argc, char *argv[])
+{
+	device_bdf = vfio_selftests_get_bdf(&argc, argv);
+	return test_harness_run(argc, argv);
+}
-- 
2.55.0.766.g2966f0265a-goog