2022-11-25 06:39:28

by Juergen Gross

[permalink] [raw]
Subject: [PATCH 0/2] x86/xen: don't return from xen_pv_play_dead()

All play_dead() functions but xen_pv_play_dead() don't return to the
caller.

Adapt xen_pv_play_dead() to behave like the other play_dead() variants.

Juergen Gross (2):
x86/xen: don't let xen_pv_play_dead() return
x86/xen: mark xen_pv_play_dead() as __noreturn

arch/x86/xen/smp.h | 2 ++
arch/x86/xen/smp_pv.c | 17 ++++-------------
arch/x86/xen/xen-head.S | 7 +++++++
tools/objtool/check.c | 1 +
4 files changed, 14 insertions(+), 13 deletions(-)

--
2.35.3


2022-11-25 06:56:26

by Juergen Gross

[permalink] [raw]
Subject: [PATCH 2/2] x86/xen: mark xen_pv_play_dead() as __noreturn

Mark xen_pv_play_dead() and related to that xen_cpu_bringup_again()
as "__noreturn".

Signed-off-by: Juergen Gross <[email protected]>
---
arch/x86/xen/smp.h | 2 +-
arch/x86/xen/smp_pv.c | 4 ++--
tools/objtool/check.c | 1 +
3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
index 6e90a312067b..22fb982ff971 100644
--- a/arch/x86/xen/smp.h
+++ b/arch/x86/xen/smp.h
@@ -21,7 +21,7 @@ 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);
+void __noreturn xen_cpu_bringup_again(unsigned long stack);

struct xen_common_irq {
int irq;
diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index b40b24382fe3..5801f93d567c 100644
--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -381,7 +381,7 @@ 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);
@@ -400,7 +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/tools/objtool/check.c b/tools/objtool/check.c
index 43ec14c29a60..becdedc2de99 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -189,6 +189,7 @@ static bool __dead_end_function(struct objtool_file *file, struct symbol *func,
"snp_abort",
"stop_this_cpu",
"usercopy_abort",
+ "xen_cpu_bringup_again",
"xen_start_kernel",
};

--
2.35.3

2022-11-25 07:01:41

by Juergen Gross

[permalink] [raw]
Subject: [PATCH 1/2] 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 <[email protected]>
---
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);

+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 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 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