[libvirt] [PATCH] qemu_process: fix starting VMs if machine group has limited cpuset.cpus

Pavel Hrdina posted 1 patch 1 week ago
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git fetch https://github.com/patchew-project/libvirt tags/patchew/7f88e4c9a8fae3196f10964eb6a5bc4b18027505.1573208385.git.phrdina@redhat.com
src/qemu/qemu_process.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

[libvirt] [PATCH] qemu_process: fix starting VMs if machine group has limited cpuset.cpus

Posted by Pavel Hrdina 1 week ago
Commit <f136b83139c63f20de0df3285d9e82df2fb97bfc> reworked process
affinity setting but did not take cgroups into account which introduced
an issue when starting VM with custom cpuset.cpus for the whole machine
group.

If the machine group is limited to some pCPUs libvirt should not try to
set a VM to run on all pCPUs as it will result in permission denied when
writing to cpuset.cpus.

To fix this the affinity has to be set separately from cgroups cpuset.

Resolves: <https://bugzilla.redhat.com/show_bug.cgi?id=1746517>

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
---
 src/qemu/qemu_process.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index ed8666e9d1..355b740caf 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2636,6 +2636,7 @@ qemuProcessSetupPid(virDomainObjPtr vm,
     virDomainNumatuneMemMode mem_mode;
     virCgroupPtr cgroup = NULL;
     virBitmapPtr use_cpumask = NULL;
+    virBitmapPtr afinity_cpumask = NULL;
     g_autoptr(virBitmap) hostcpumap = NULL;
     char *mem_mask = NULL;
     int ret = -1;
@@ -2661,7 +2662,7 @@ qemuProcessSetupPid(virDomainObjPtr vm,
          * its config file */
         if (qemuProcessGetAllCpuAffinity(&hostcpumap) < 0)
             goto cleanup;
-        use_cpumask = hostcpumap;
+        afinity_cpumask = hostcpumap;
     }
 
     /*
@@ -2702,8 +2703,11 @@ qemuProcessSetupPid(virDomainObjPtr vm,
 
     }
 
+    if (!afinity_cpumask)
+        afinity_cpumask = use_cpumask;
+
     /* Setup legacy affinity. */
-    if (use_cpumask && virProcessSetAffinity(pid, use_cpumask) < 0)
+    if (afinity_cpumask && virProcessSetAffinity(pid, afinity_cpumask) < 0)
         goto cleanup;
 
     /* Set scheduler type and priority, but not for the main thread. */
-- 
2.23.0

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Re: [libvirt] [PATCH] qemu_process: fix starting VMs if machine group has limited cpuset.cpus

Posted by Michal Privoznik 2 days ago
On 11/8/19 11:20 AM, Pavel Hrdina wrote:
> Commit <f136b83139c63f20de0df3285d9e82df2fb97bfc> reworked process
> affinity setting but did not take cgroups into account which introduced
> an issue when starting VM with custom cpuset.cpus for the whole machine
> group.
> 
> If the machine group is limited to some pCPUs libvirt should not try to
> set a VM to run on all pCPUs as it will result in permission denied when
> writing to cpuset.cpus.
> 
> To fix this the affinity has to be set separately from cgroups cpuset.
> 
> Resolves: <https://bugzilla.redhat.com/show_bug.cgi?id=1746517>
> 
> Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
> ---
>   src/qemu/qemu_process.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)

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

Michal

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