x86/xen: don't let xen_pv_play_dead() return

A function called via the paravirt play_dead() hook should not return
to the caller.

xen_pv_play_dead() has a problem in this regard, as it currently will
return in case an offlined cpu is brought to life again. This can be
changed only by doing basically a longjmp() to cpu_bringup_and_idle(),
as the hypercall for bringing down the cpu will just return when the
cpu is coming up again. Just re-initializing the cpu isn't possible,
as the Xen hypervisor will deny that operation.

So introduce xen_cpu_bringup_again() resetting the stack and calling
cpu_bringup_and_idle(), which can be called after HYPERVISOR_vcpu_op()
in xen_pv_play_dead().

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221125063248.30256-2-jgross@suse.com
Signed-off-by: Juergen Gross <jgross@suse.com>

diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
index bd02f9d..6e90a31 100644 (file)
--- a/arch/x86/xen/smp.h
+++ b/arch/x86/xen/smp.h
@@ -21,6 +21,8 @@ void xen_smp_send_reschedule(int cpu);
 void xen_smp_send_call_function_ipi(const struct cpumask *mask);
 void xen_smp_send_call_function_single_ipi(int cpu);
 
+void xen_cpu_bringup_again(unsigned long stack);
+
 struct xen_common_irq {
        int irq;
        char *name;

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index 6175f2c..a97b050 100644 (file)
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -385,17 +385,8 @@ static void xen_pv_play_dead(void) /* used only with HOTPLUG_CPU */
 {
        play_dead_common();
        HYPERVISOR_vcpu_op(VCPUOP_down, xen_vcpu_nr(smp_processor_id()), NULL);
-       cpu_bringup();
-       /*
-        * commit 4b0c0f294 (tick: Cleanup NOHZ per cpu data on cpu down)
-        * clears certain data that the cpu_idle loop (which called us
-        * and that we return from) expects. The only way to get that
-        * data back is to call:
-        */
-       tick_nohz_idle_enter();
-       tick_nohz_idle_stop_tick_protected();
-
-       cpuhp_online_idle(CPUHP_AP_ONLINE_IDLE);
+       xen_cpu_bringup_again((unsigned long)task_pt_regs(current));
+       BUG();
 }
 
 #else /* !CONFIG_HOTPLUG_CPU */

diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S
index ffaa621..e36ea42 100644 (file)
--- a/arch/x86/xen/xen-head.S
+++ b/arch/x86/xen/xen-head.S
@@ -76,6 +76,13 @@ SYM_CODE_START(asm_cpu_bringup_and_idle)
 
        call cpu_bringup_and_idle
 SYM_CODE_END(asm_cpu_bringup_and_idle)
+
+SYM_CODE_START(xen_cpu_bringup_again)
+       UNWIND_HINT_FUNC
+       mov     %rdi, %rsp
+       UNWIND_HINT_REGS
+       call    cpu_bringup_and_idle
+SYM_CODE_END(xen_cpu_bringup_again)
 .popsection
 #endif
 #endif