From patchwork Tue Aug 14 11:43:12 2012
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Subject: [v2,uq/master] kvmvapic: Disable if there is insufficient memory
Date: Tue, 14 Aug 2012 01:43:12 -0000
From: Jan Kiszka <jan.kiszka@siemens.com>
X-Patchwork-Id: 177233
Message-Id: <502A39D0.7080702@siemens.com>
To: Avi Kivity <avi@redhat.com>, Marcelo Tosatti <mtosatti@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>, kvm <kvm@vger.kernel.org>,
 qemu-devel <qemu-devel@nongnu.org>

We need at least 1M of RAM to map the option ROM. Otherwise, we will
corrupt host memory or even crash:

    $ qemu-system-x86_64 -nodefaults --enable-kvm -vnc :0 -m 640k
    Segmentation fault (core dumped)

Reported-and-tested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

---
hw/apic_common.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/hw/apic_common.c b/hw/apic_common.c
index 58e63b0..371f95d 100644
--- a/hw/apic_common.c
+++ b/hw/apic_common.c
@@ -299,7 +299,9 @@ static int apic_init_common(SysBusDevice *dev)
 
     sysbus_init_mmio(dev, &s->io_memory);
 
-    if (!vapic && s->vapic_control & VAPIC_ENABLE_MASK) {
+    /* Note: We need at least 1M to map the VAPIC option ROM */
+    if (!vapic && s->vapic_control & VAPIC_ENABLE_MASK &&
+        ram_size >= 1024 * 1024) {
         vapic = sysbus_create_simple("kvmvapic", -1, NULL);
     }
     s->vapic = vapic;