[PATCH v9 5/5] vfio: selftests: igb: Recover after DMA-read faults

[Josh Hilke]

From: Alex Williamson <alex.williamson@xxxxxxxxxx>

The mix_and_match test intentionally submits a TX descriptor with an
unmapped source IOVA so that the DMA read fails.  On real 82576
hardware the resulting fault leaves the descriptor engine unable to
service subsequent valid descriptors, so the next memcpy in the same
test iteration times out.

The 82576 datasheet (section 4.2.1.6.1) describes CTRL.RST as the
software mechanism to recover from a hung device.  Empirically
CTRL.RST alone is not sufficient in this state: the visible queue
registers are reinitialized, but the next valid memcpy still posts
descriptors without any TDH/TDT progress in the same process.  A
fresh device open after the failure works, which points to a reset
scope broader than CTRL.RST being required.  The 82576 advertises
PCIe FLR; VFIO_DEVICE_RESET drives FLR and supplies that scope while
preserving the selftest process and its DMA mappings.

Add igb_error_reset_and_reinit() implementing the recovery sequence:
issue VFIO_DEVICE_RESET, re-arm the kernel-side MSI-X trigger against
the still-valid eventfd via vfio_pci_irq_reenable() (this does not
touch the eventfd, which test fixtures may have cached), and
re-program the device via igb_hw_init().  FLR clears EICR and leaves
EIMS=0, so no explicit interrupt mask or cause writes are needed.
igb_hw_init() resets tx_tail/rx_tail to 0 and igb_memcpy_start() zeros
each descriptor before submission, so no ring memset is needed either.

Call this from igb_memcpy_wait() on completion timeout. Lock contention
during reset (e.g. if PCIe/IOMMU/AER error handling triggered by the
just-observed DMA fault holds the device lock) is handled by the retry
logic now present inside vfio_pci_device_reset(). The failed memcpy still
returns -ETIMEDOUT; reset recovery only ensures the next operation starts
from a usable device state.

Assisted-by: Claude:claude-opus-4-7
Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
---
 tools/testing/selftests/vfio/lib/drivers/igb/igb.c | 38 +++++++++++++++++++++-
 1 file changed, 37 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/vfio/lib/drivers/igb/igb.c b/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
index ac7b52d89757..97a2f29aade3 100644
--- a/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
+++ b/tools/testing/selftests/vfio/lib/drivers/igb/igb.c
@@ -478,6 +478,28 @@ static void igb_memcpy_start(struct vfio_pci_device *device, iova_t src,
 	igb_write32(igb, E1000_TDT(0), igb->tx_tail);
 }
 
+/*
+ * Reset the device via VFIO_DEVICE_RESET (PCIe FLR on the 82576) and
+ * re-program it.  VFIO_DEVICE_RESET tears down the kernel-side MSI-X
+ * trigger but leaves user-side eventfds intact, so re-arm the trigger
+ * via vfio_pci_irq_reenable() before reprogramming so any caller-cached
+ * eventfd remains valid.
+ *
+ * FLR clears device-side state to power-on reset values (datasheet
+ * 4.2.1.5.1: a PF FLR is "equivalent to a D0->D3->D0 transition"), so
+ * EIMS and EICR come back as 0 from their register-defined initial
+ * values, and igb_hw_init() resets tx_tail/rx_tail to 0.  The next
+ * igb_memcpy_start() will memset each descriptor it touches before
+ * submission, so no explicit IMC/EICR writes or ring memsets are
+ * needed here.
+ */
+static void igb_error_reset_and_reinit(struct vfio_pci_device *device)
+{
+	vfio_pci_device_reset(device);
+	vfio_pci_msix_reenable(device, MSIX_VECTOR, 1);
+	igb_hw_init(device);
+}
+
 static int igb_memcpy_wait(struct vfio_pci_device *device)
 {
 	struct igb *igb = to_igb_state(device);
@@ -520,7 +542,21 @@ static int igb_memcpy_wait(struct vfio_pci_device *device)
 
 	igb_irq_enable(igb);
 
-	return (status & 1) ? 0 : -ETIMEDOUT;
+	if (status & 1)
+		return 0;
+
+	/*
+	 * The descriptor never completed.  On real 82576 hardware this
+	 * typically follows a DMA-read fault from one of the intentional
+	 * unmapped-IOVA tests; the fault leaves the descriptor engine
+	 * unable to service subsequent valid descriptors.  CTRL.RST alone
+	 * reinitializes the queue registers but leaves the engine wedged
+	 * for the current process, so a broader VFIO_DEVICE_RESET (FLR)
+	 * is required.
+	 */
+	igb_error_reset_and_reinit(device);
+
+	return -ETIMEDOUT;
 }
 
 static void igb_send_msi(struct vfio_pci_device *device)

-- 
2.55.0.508.g3f0d502094-goog