From 133c1cc45c7289d0a9d777503294feec907ac54e 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>

diff --git a/hw/misc/vfio.c b/hw/misc/vfio.c
index 0b9eba0..7beee5e 100644
--- a/hw/misc/vfio.c
+++ b/hw/misc/vfio.c
@@ -253,6 +253,7 @@ static const VFIORomBlacklistEntry romblacklist[] = {
 };
 
 #define MSIX_CAP_LENGTH 12
+#define MAX_DEV_ASSIGN_CMDLINE 32
 
 static QLIST_HEAD(, VFIOGroup)
     group_list = QLIST_HEAD_INITIALIZER(group_list);
@@ -4153,7 +4154,19 @@ static int vfio_initfn(PCIDevice *pdev)
     ssize_t len;
     struct stat st;
     int groupid;
-    int ret;
+    int ret, i = 0;
+
+    QLIST_FOREACH(group, &group_list, next) {
+        QLIST_FOREACH(pvdev, &group->device_list, next) {
+            i++;
+        }
+    }
+
+    if (i >= MAX_DEV_ASSIGN_CMDLINE) {
+        error_report("vfio: Maximum supported vfio devices (%d) "
+                     "already attached\n", MAX_DEV_ASSIGN_CMDLINE);
+        return -1;
+    }
 
     /* Check that the host device exists */
     snprintf(path, sizeof(path),