From ac89574e251dfecf34606083e402194ded63dba2 Mon Sep 17 00:00:00 2001

Message-Id: <ac89574e251dfecf34606083e402194ded63dba2@dist-git>

From: Michal Privoznik <mprivozn@redhat.com>

Date: Wed, 5 Jun 2019 11:33:29 +0200

Subject: [PATCH] qemu: Set up EMULATOR thread and cpuset.mems before

 exec()-ing qemu

It's funny how this went unnoticed for such a long time. Long

story short, if a domain is configured with

VIR_DOMAIN_NUMATUNE_MEM_STRICT libvirt doesn't really honour

that. This is because of 7e72ac787848 after which libvirt allowed

qemu to allocate memory just anywhere and only after that it used

some magic involving cpuset.memory_migrate and cpuset.mems to

move the memory to desired NUMA nodes. This was done in order to

work around some KVM bug where KVM would fail if there wasn't a

DMA zone available on the NUMA node. Well, while the work around

might stopped libvirt tickling the KVM bug it also caused a bug

on libvirt side: if there is not enough memory on configured NUMA

node(s) then any attempt to start a domain must fail. Because of

the way we play with guest memory domains can start just happily.

The solution is to move the child we've just forked into emulator

cgroup, set up cpuset.mems and exec() qemu only after that.

This basically reverts 7e72ac787848b7434c9 which was a workaround

for kernel bug. This bug was apparently fixed because I've tested

this successfully with recent kernel.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

Reviewed-by: Martin Kletzander <mkletzan@redhat.com>

(cherry picked from commit 0eaa4716e1b8f6eb59d77049aed3735c3b5fbdd6)

https://bugzilla.redhat.com/show_bug.cgi?id=1716943

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

Message-Id: <fe479c5bad92778ec29f1c1bf4fb0c7b9049f3ab.1559727075.git.mprivozn@redhat.com>

Reviewed-by: Andrea Bolognani <abologna@redhat.com>

---

 src/qemu/qemu_process.c | 8 ++++----

 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c

index 6071b3ba3d..8b05cef80c 100644

--- a/src/qemu/qemu_process.c

+++ b/src/qemu/qemu_process.c

@@ -6442,6 +6442,10 @@ qemuProcessLaunch(virConnectPtr conn,

     if (qemuProcessInitCpuAffinity(vm) < 0)

         goto cleanup;

+    VIR_DEBUG("Setting emulator tuning/settings");

+    if (qemuProcessSetupEmulator(vm) < 0)

+        goto cleanup;

+

     VIR_DEBUG("Setting cgroup for external devices (if required)");

     if (qemuSetupCgroupForExtDevices(vm, driver) < 0)

         goto cleanup;

@@ -6533,10 +6537,6 @@ qemuProcessLaunch(virConnectPtr conn,

     if (qemuProcessDetectIOThreadPIDs(driver, vm, asyncJob) < 0)

         goto cleanup;

-    VIR_DEBUG("Setting emulator tuning/settings");

-    if (qemuProcessSetupEmulator(vm) < 0)

-        goto cleanup;

-

     VIR_DEBUG("Setting global CPU cgroup (if required)");

     if (qemuSetupGlobalCpuCgroup(vm) < 0)

         goto cleanup;

-- 

2.22.0