From 3cb35556dc7d994f203d732fe952f95fcdb03c0a Mon Sep 17 00:00:00 2001
From: Bandan Das <bsd@redhat.com>
Date: Tue, 3 Dec 2013 20:05:13 +0100
Subject: vfio: cap number of devices that can be assigned

RH-Author: Bandan Das <bsd@redhat.com>
Message-id: <1386101113-31560-3-git-send-email-bsd@redhat.com>
Patchwork-id: 55984
O-Subject: [PATCH RHEL7 qemu-kvm v2 2/2] vfio: cap number of devices that can be assigned
Bugzilla: 678368
RH-Acked-by: Alex Williamson <alex.williamson@redhat.com>
RH-Acked-by: Marcelo Tosatti <mtosatti@redhat.com>
RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>

Go through all groups to get count of total number of devices
active to enforce limit

Reasoning from Alex for the limit(32) - Assuming 3 slots per
device, with 125 slots (number of memory slots for RHEL 7),
we can support almost 40 devices and still have few slots left
for other uses. Stepping down a bit, the number 32 arbitrarily
matches the number of slots on a PCI bus and is also a nice power
of two.

Signed-off-by: Bandan Das <bsd@redhat.com>

Rebase notes (2.8.0):
- removed return value for vfio_realize (commit 1a22aca)

Merged patches (2.9.0):
- 17eb774 vfio: Use error_setg when reporting max assigned device overshoot

(cherry picked from commit 9fa3c9fc6dfcde76d80db1aa601b2d577f72ceec)
---
 hw/vfio/pci.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
index 31e1edf..f3f1ce6 100644
--- a/hw/vfio/pci.c
+++ b/hw/vfio/pci.c
@@ -34,6 +34,7 @@
 #include "qapi/error.h"
 
 #define MSIX_CAP_LENGTH 12
+#define MAX_DEV_ASSIGN_CMDLINE 32
 
 static void vfio_disable_interrupts(VFIOPCIDevice *vdev);
 static void vfio_mmap_set_enabled(VFIOPCIDevice *vdev, bool enabled);
@@ -2639,7 +2640,19 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
     ssize_t len;
     struct stat st;
     int groupid;
-    int i, ret;
+    int ret, i = 0;
+
+    QLIST_FOREACH(group, &vfio_group_list, next) {
+        QLIST_FOREACH(vbasedev_iter, &group->device_list, next) {
+            i++;
+        }
+    }
+
+    if (i >= MAX_DEV_ASSIGN_CMDLINE) {
+        error_setg(errp, "Maximum supported vfio devices (%d) "
+                     "already attached", MAX_DEV_ASSIGN_CMDLINE);
+        return;
+    }
 
     if (!vdev->vbasedev.sysfsdev) {
         if (!(~vdev->host.domain || ~vdev->host.bus ||
-- 
1.8.3.1