[PATCH 2/2] qemu_capabilities.c: drop 'kvm_pr' support for non-Power8 hosts
PPC64 has two KVM modules: kvm_hv and kvm_pr. The official supported
module was always kvm_hv, while kvm_pr was used for internal testing
or for very niche cases in Power 8 hosts, always without official
IBM or distro support.
Problem is, QMP will report KVM supportfor PPC64 if any of these
modules is loaded in the host, and kvm_pr is broken in everything
but Power8 (and will remain broken, since kvm_pr is unmaintained).
This can lead to situations like [1], where the tooling is misled to
believe that the host has KVM capabilities when in reality it
doesn't.
The first reaction would be to simply forsake kvm_pr support entirely
and move on, but there is no reason for now to be disruptive with any
Power8 guests in the wild that are using kvm_pr (somehow). A more
subtle approach is to not claim QEMU_CAPS_KVM support in all cases
that we know it's completely broken, allowing Power8 users to take
their shot using kvm_pr in their VMs. We can remove kvm_pr support
completely when the module is removed from the kernel.
[1] https://bugzilla.redhat.com/show_bug.cgi?id=1843865
CC: Leonardo Augusto Guimarães Garcia <lagarcia(a)br.ibm.com>
CC: Greg Kurz <groug(a)kaod.org>
CC: David Gibson <david(a)gibson.dropbear.id.au>
CC: Richard W.M. Jones <rjones(a)redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413(a)gmail.com>
---
src/qemu/qemu_capabilities.c | 38 ++++++++++++++++++++++++++++++++++--
1 file changed, 36 insertions(+), 2 deletions(-)
diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 484fff99e5..b1c1d4dd70 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -49,6 +49,7 @@
#include "qemu_process.h"
#include "qemu_firmware.h"
#include "virutil.h"
+#include "virkmod.h"
#include <fcntl.h>
#include <sys/stat.h>
@@ -3242,6 +3243,31 @@ virQEMUCapsProbeQMPTPM(virQEMUCapsPtr qemuCaps,
}
+static void
+virQEMUCapsSetPPC64KVMState(virQEMUCapsPtr qemuCaps, virArch hostArch)
+{
+ g_autoptr(virCPUDef) hostCPU = virCPUProbeHost(hostArch);
+
+ /* At this moment, PPC64 has two KVM modules: kvm_hv and kvm_pr.
+ * QEMU will return KVM present and enabled = true if any of these
+ * is loaded in the host. Thing is, kvm_pr was never officially
+ * supported by IBM or any other distro, but people still ended
+ * up using it in Power8 hosts regardless. It is also currently
+ * unmaintained and broken on Power9, and will be sunset in the
+ * future. kvm_hv is the only KVM module that is and will be
+ * supported.
+ *
+ * Until then, do not claim QEMU_CAPS_KVM if there is only kvm_pr
+ * loaded in the host. There is a good chance that there are
+ * unsupported kvm_pr Power8 guests running in the wild, so let's
+ * cut some slack for this case, for now. */
+ if (STRNEQLEN(hostCPU->model, "POWER8", 6) &&
!virKModIsLoaded("kvm_hv"))
+ return;
+
+ virQEMUCapsSet(qemuCaps, QEMU_CAPS_KVM);
+}
+
+
static int
virQEMUCapsProbeQMPKVMState(virQEMUCapsPtr qemuCaps,
qemuMonitorPtr mon)
@@ -3252,8 +3278,16 @@ virQEMUCapsProbeQMPKVMState(virQEMUCapsPtr qemuCaps,
if (qemuMonitorGetKVMState(mon, &enabled, &present) < 0)
return -1;
- if (present && enabled)
- virQEMUCapsSet(qemuCaps, QEMU_CAPS_KVM);
+ if (present && enabled) {
+ virArch hostArch = virArchFromHost();
+
+ if (ARCH_IS_PPC64(hostArch)) {
+ virQEMUCapsSetPPC64KVMState(qemuCaps, hostArch);
+ return 0;
+ }
+
+ virQEMUCapsSet(qemuCaps, QEMU_CAPS_KVM);
+ }
return 0;
}
--
2.26.2