Commit 336f560a authored by Juergen Gross's avatar Juergen Gross
Browse files

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: default avatarJuergen Gross <jgross@suse.com>
Reviewed-by: default avatarBoris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20221125063248.30256-2-jgross@suse.com


Signed-off-by: default avatarJuergen Gross <jgross@suse.com>
parent 415dab3c

arch/x86/xen/smp.h

+2 −0
Original line number Diff line number Diff line
@@ -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;

arch/x86/xen/smp_pv.c

+2 −11
Original line number Diff line number Diff line
@@ -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 */

arch/x86/xen/xen-head.S

+7 −0
Original line number Diff line number Diff line
@@ -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