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Peter Anvin" , xen-devel@lists.xenproject.org Subject: [PATCH 1/2] x86/xen: don't let xen_pv_play_dead() return Date: Fri, 25 Nov 2022 07:32:47 +0100 Message-Id: <20221125063248.30256-2-jgross@suse.com> X-Mailer: git-send-email 2.35.3 In-Reply-To: <20221125063248.30256-1-jgross@suse.com> References: <20221125063248.30256-1-jgross@suse.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMail-DKIM: pass (identity @suse.com) X-ZM-MESSAGEID: 1669358010626100003 Content-Type: text/plain; charset="utf-8" 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 --- arch/x86/xen/smp.h | 2 ++ arch/x86/xen/smp_pv.c | 13 ++----------- arch/x86/xen/xen-head.S | 7 +++++++ 3 files changed, 11 insertions(+), 11 deletions(-) diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h index bd02f9d50107..6e90a312067b 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); =20 +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 480be82e9b7b..b40b24382fe3 100644 --- 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 H= OTPLUG_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(); } =20 #else /* !CONFIG_HOTPLUG_CPU */ 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) =20 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 --=20 2.35.3