| Message ID | 20221114160150.13554-1-ldufour@linux.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | f6aa37c51ec0d053ee34c235bfe0e666618a3baf |
| Headers | show |
| Series | powerpc/pseries: unregister VPA when hot unplugging a CPU | expand |
| Context | Check | Description |
|---|---|---|
| snowpatch_ozlabs/github-powerpc_selftests | success | Successfully ran 8 jobs. |
| snowpatch_ozlabs/github-powerpc_ppctests | success | Successfully ran 8 jobs. |
| snowpatch_ozlabs/github-powerpc_sparse | success | Successfully ran 4 jobs. |
| snowpatch_ozlabs/github-powerpc_clang | success | Successfully ran 6 jobs. |
Laurent Dufour <ldufour@linux.ibm.com> writes: > The VPA should unregister when offlining a CPU. Otherwise there could be a > short window where 2 CPUs could share the same VPA. > > This happens because the hypervisor is still keeping the VPA attached to > the vCPU even if it became offline. > > Here is a potential situation: > 1. remove proc A, > 2. add proc B. If proc B gets proc A's place in cpu_present_map, then it > registers proc A's VPAs. > 3. If proc B is then re-added to the LP, its threads are sharing VPAs with > proc A briefly as they come online. > > As the hypervisor may check for the VPA's yield_count field oddity, it may > detects an unexpected value and kill the LPAR. > > Suggested-by: Nathan Lynch <nathanl@linux.ibm.com> > Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> > --- > arch/powerpc/platforms/pseries/hotplug-cpu.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c > index e0a7ac5db15d..090ae5a1e0f5 100644 > --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c > +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c > @@ -70,6 +70,7 @@ static void pseries_cpu_offline_self(void) > xics_teardown_cpu(); > > unregister_slb_shadow(hwcpu); > + unregister_vpa(hwcpu); > rtas_stop_self(); > > /* Should never get here... */ Reviewed-by: Nathan Lynch <nathanl@linux.ibm.com> I was wondering whether we could leave an active dispatch trace log buffer registered, which could interfere with releasing the VPA, but I verified that DTL has the appropriate cpuhp callback for that (dtl_worker_offline()). Alternatively we could change the code to dynamically register and unregister VPAs only on processor add and remove, as opposed to CPU online/offline. But I can't see any significant advantage to that.
On Mon, 14 Nov 2022 17:01:50 +0100, Laurent Dufour wrote: > The VPA should unregister when offlining a CPU. Otherwise there could be a > short window where 2 CPUs could share the same VPA. > > This happens because the hypervisor is still keeping the VPA attached to > the vCPU even if it became offline. > > Here is a potential situation: > 1. remove proc A, > 2. add proc B. If proc B gets proc A's place in cpu_present_map, then it > registers proc A's VPAs. > 3. If proc B is then re-added to the LP, its threads are sharing VPAs with > proc A briefly as they come online. > > [...] Applied to powerpc/next. [1/1] powerpc/pseries: unregister VPA when hot unplugging a CPU https://git.kernel.org/powerpc/c/f6aa37c51ec0d053ee34c235bfe0e666618a3baf cheers
diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c index e0a7ac5db15d..090ae5a1e0f5 100644 --- a/arch/powerpc/platforms/pseries/hotplug-cpu.c +++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c @@ -70,6 +70,7 @@ static void pseries_cpu_offline_self(void) xics_teardown_cpu(); unregister_slb_shadow(hwcpu); + unregister_vpa(hwcpu); rtas_stop_self(); /* Should never get here... */
The VPA should unregister when offlining a CPU. Otherwise there could be a short window where 2 CPUs could share the same VPA. This happens because the hypervisor is still keeping the VPA attached to the vCPU even if it became offline. Here is a potential situation: 1. remove proc A, 2. add proc B. If proc B gets proc A's place in cpu_present_map, then it registers proc A's VPAs. 3. If proc B is then re-added to the LP, its threads are sharing VPAs with proc A briefly as they come online. As the hypervisor may check for the VPA's yield_count field oddity, it may detects an unexpected value and kill the LPAR. Suggested-by: Nathan Lynch <nathanl@linux.ibm.com> Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com> --- arch/powerpc/platforms/pseries/hotplug-cpu.c | 1 + 1 file changed, 1 insertion(+)