[Xen-devel] [PATCH] xen/pvhsim: fix cpu onlining

Juergen Gross posted 1 patch 4 years, 5 months ago
Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/xen tags/patchew/20191023121209.4814-1-jgross@suse.com
There is a newer version of this series
xen/arch/x86/pv/shim.c |  2 ++
xen/common/schedule.c  | 11 +++++------
2 files changed, 7 insertions(+), 6 deletions(-)
[Xen-devel] [PATCH] xen/pvhsim: fix cpu onlining
Posted by Juergen Gross 4 years, 5 months ago
Since commit 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
the initial processor for all pv-shim vcpus will be 0, as no other cpus
are online when the vcpus are created. Before that commit the vcpus
would have processors set not being online yet, which worked just by
chance.

When the pv-shim vcpu becomes active it will have a hard affinity
not matching its initial processor assignment leading to failing
ASSERT()s or other problems depending on the selected scheduler.

Fix that by doing the affinity setting after onlining the cpu but
before taking the vcpu up. For vcpu 0 this is still in
sched_setup_dom0_vcpus(), for the other vcpus setting the affinity
there can be dropped.

Fixes: 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
Reported-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Tested-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
---
 xen/arch/x86/pv/shim.c |  2 ++
 xen/common/schedule.c  | 11 +++++------
 2 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
index 5edbcd9ac5..4329eaaefe 100644
--- a/xen/arch/x86/pv/shim.c
+++ b/xen/arch/x86/pv/shim.c
@@ -837,6 +837,8 @@ long pv_shim_cpu_up(void *data)
                     v->vcpu_id, rc);
             return rc;
         }
+
+        vcpu_set_hard_affinity(v, cpumask_of(v->vcpu_id));
     }
 
     wake = test_and_clear_bit(_VPF_down, &v->pause_flags);
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index c327c40b92..326f4d3601 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -3102,13 +3102,12 @@ void __init sched_setup_dom0_vcpus(struct domain *d)
     for ( i = 1; i < d->max_vcpus; i++ )
         vcpu_create(d, i);
 
-    for_each_sched_unit ( d, unit )
+    if ( pv_shim )
+        sched_set_affinity(d->vcpu[0]->sched_unit,
+                           cpumask_of(0), cpumask_of(0));
+    else
     {
-        unsigned int id = unit->unit_id;
-
-        if ( pv_shim )
-            sched_set_affinity(unit, cpumask_of(id), cpumask_of(id));
-        else
+        for_each_sched_unit ( d, unit )
         {
             if ( !opt_dom0_vcpus_pin && !dom0_affinity_relaxed )
                 sched_set_affinity(unit, &dom0_cpus, NULL);
-- 
2.16.4


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Re: [Xen-devel] [PATCH] xen/pvhsim: fix cpu onlining
Posted by Roger Pau Monné 4 years, 5 months ago
On Wed, Oct 23, 2019 at 02:12:09PM +0200, Juergen Gross wrote:
> Since commit 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
> the initial processor for all pv-shim vcpus will be 0, as no other cpus
> are online when the vcpus are created. Before that commit the vcpus
> would have processors set not being online yet, which worked just by
> chance.
> 
> When the pv-shim vcpu becomes active it will have a hard affinity
> not matching its initial processor assignment leading to failing
> ASSERT()s or other problems depending on the selected scheduler.
> 
> Fix that by doing the affinity setting after onlining the cpu but
> before taking the vcpu up. For vcpu 0 this is still in
> sched_setup_dom0_vcpus(), for the other vcpus setting the affinity
> there can be dropped.
> 
> Fixes: 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
> Reported-by: Sergey Dyasli <sergey.dyasli@citrix.com>
> Tested-by: Sergey Dyasli <sergey.dyasli@citrix.com>
> Signed-off-by: Juergen Gross <jgross@suse.com>

Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Thanks.

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Re: [Xen-devel] [PATCH] xen/pvhsim: fix cpu onlining
Posted by Jan Beulich 4 years, 5 months ago
On 23.10.2019 14:55, Roger Pau Monné wrote:
> On Wed, Oct 23, 2019 at 02:12:09PM +0200, Juergen Gross wrote:
>> Since commit 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
>> the initial processor for all pv-shim vcpus will be 0, as no other cpus
>> are online when the vcpus are created. Before that commit the vcpus
>> would have processors set not being online yet, which worked just by
>> chance.
>>
>> When the pv-shim vcpu becomes active it will have a hard affinity
>> not matching its initial processor assignment leading to failing
>> ASSERT()s or other problems depending on the selected scheduler.
>>
>> Fix that by doing the affinity setting after onlining the cpu but
>> before taking the vcpu up. For vcpu 0 this is still in
>> sched_setup_dom0_vcpus(), for the other vcpus setting the affinity
>> there can be dropped.
>>
>> Fixes: 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
>> Reported-by: Sergey Dyasli <sergey.dyasli@citrix.com>
>> Tested-by: Sergey Dyasli <sergey.dyasli@citrix.com>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

Acked-by: Jan Beulich <jbeulich@suse.com>

I have to admit though that I miss a comment on the pv_shim
conditional in schedule.c - such a special case shouldn't
really be there, but since it's needed it should be explained.
I realize though that the patch here only moves the special
case, i.e. the lack of comment is pre-existing.

Jan

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Re: [Xen-devel] [PATCH] xen/pvhsim: fix cpu onlining
Posted by Jürgen Groß 4 years, 5 months ago
On 23.10.19 14:55, Roger Pau Monné wrote:
> On Wed, Oct 23, 2019 at 02:12:09PM +0200, Juergen Gross wrote:
>> Since commit 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
>> the initial processor for all pv-shim vcpus will be 0, as no other cpus
>> are online when the vcpus are created. Before that commit the vcpus
>> would have processors set not being online yet, which worked just by
>> chance.
>>
>> When the pv-shim vcpu becomes active it will have a hard affinity
>> not matching its initial processor assignment leading to failing
>> ASSERT()s or other problems depending on the selected scheduler.
>>
>> Fix that by doing the affinity setting after onlining the cpu but
>> before taking the vcpu up. For vcpu 0 this is still in
>> sched_setup_dom0_vcpus(), for the other vcpus setting the affinity
>> there can be dropped.
>>
>> Fixes: 8d3c326f6756d1 ("xen: let vcpu_create() select processor")
>> Reported-by: Sergey Dyasli <sergey.dyasli@citrix.com>
>> Tested-by: Sergey Dyasli <sergey.dyasli@citrix.com>
>> Signed-off-by: Juergen Gross <jgross@suse.com>
> 
> Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

And just for the protocol:

Release-acked-by: Juergen Gross <jgross@suse.com>


Juergen

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