From: Alex Williamson <alex.williamson@redhat.com>
Date: Thu, 16 May 2024 11:48:30 -0600
Subject: vfio/pci: Restore zero affected bus reset devices warning
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Git-commit: cbb325e77fbe62a06184175aa98c9eb98736c3e8
Patch-mainline: v6.10-rc1
References: jsc#PED-10968

Yi notes relative to commit f6944d4a0b87 ("vfio/pci: Collect hot-reset
devices to local buffer") that we previously tested the resulting
device count with a WARN_ON, which was removed when we switched to
the in-loop user copy in commit b56b7aabcf3c ("vfio/pci: Copy hot-reset
device info to userspace in the devices loop").  Finding no devices in
the bus/slot would be an unexpected condition, so let's restore the
warning and trigger a -ERANGE error here as success with no devices
would be an unexpected result to userspace as well.

Suggested-by: Yi Liu <yi.l.liu@intel.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Reviewed-by: Yi Liu <yi.l.liu@intel.com>
Link: https://lore.kernel.org/r/20240516174831.2257970-1-alex.williamson@redhat.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Acked-by: Joerg Roedel <jroedel@suse.de>
---
 drivers/vfio/pci/vfio_pci_core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
index d8c95cc16be8..80cae87fff36 100644
--- a/drivers/vfio/pci/vfio_pci_core.c
+++ b/drivers/vfio/pci/vfio_pci_core.c
@@ -1281,6 +1281,9 @@ static int vfio_pci_ioctl_get_pci_hot_reset_info(
 	if (ret)
 		return ret;
 
+	if (WARN_ON(!count)) /* Should always be at least one */
+		return -ERANGE;
+
 	if (count > (hdr.argsz - sizeof(hdr)) / sizeof(*devices)) {
 		hdr.count = count;
 		ret = -ENOSPC;

