From 7ebb76ec0ed32b657ceda530b620ef563ac0f212 Mon Sep 17 00:00:00 2001 From: Juergen Gross Date: Thu, 24 Nov 2022 08:09:45 +0100 Subject: [PATCH] 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(). Annotate xen_pv_play_dead() and xen_cpu_bringup_again() with "__noreturn". Signed-off-by: Juergen Gross --- arch/x86/xen/smp.h | 2 ++ arch/x86/xen/smp_pv.c | 17 ++++------------- arch/x86/xen/xen-head.S | 7 +++++++ 3 files changed, 13 insertions(+), 13 deletions(-) diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h index bd02f9d50107..22fb982ff971 100644 --- 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 __noreturn 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 480be82e9b7b..5801f93d567c 100644 --- a/arch/x86/xen/smp_pv.c +++ b/arch/x86/xen/smp_pv.c @@ -381,21 +381,12 @@ static void xen_pv_cpu_die(unsigned int cpu) } } -static void xen_pv_play_dead(void) /* used only with HOTPLUG_CPU */ +static void __noreturn 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 */ @@ -409,7 +400,7 @@ static void xen_pv_cpu_die(unsigned int cpu) BUG(); } -static void xen_pv_play_dead(void) +static void __noreturn xen_pv_play_dead(void) { BUG(); } diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S index ffaa62167f6e..e36ea4268bd2 100644 --- 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 -- 2.35.3