[PATCH 4/5] xen/vcpu: Handle xen_vcpu_setup() failure in hotplug
From: Ankur Arora
Date: Fri Jun 02 2017 - 20:06:57 EST
The hypercall VCPUOP_register_vcpu_info can fail. This failure is
handled by making per_cpu(xen_vcpu, cpu) point to its shared_info
slot and those without one (cpu >= MAX_VIRT_CPUS) be NULL.
For PVH/PVHVM, this is not enough, because we also need to pull
these VCPUs out of circulation.
Fix for PVH/PVHVM: on registration failure in the cpuhp prepare
callback (xen_cpu_up_prepare_hvm()), return an error to the cpuhp
state-machine so it can fail the CPU init.
Fix for PV: the registration happens before smp_init(), so, in the
failure case we clamp setup_max_cpus and limit the number of VCPUs
that smp_init() will bring-up to MAX_VIRT_CPUS.
This is functionally correct but it makes the code a bit simpler
if we get rid of this explicit clamping: for VCPUs that don't have
valid xen_vcpu, fail the CPU init in the cpuhp prepare callback
(xen_cpu_up_prepare_pv()).
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Signed-off-by: Ankur Arora <ankur.a.arora@xxxxxxxxxx>
---
arch/x86/xen/enlighten.c | 46 +++++++++++++++++++++++++-------------------
arch/x86/xen/enlighten_hvm.c | 9 +++++----
arch/x86/xen/enlighten_pv.c | 14 +++++++++++++-
arch/x86/xen/xen-ops.h | 2 +-
4 files changed, 45 insertions(+), 26 deletions(-)
diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 276cc21619ec..0e7ef69e8531 100644
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -106,8 +106,10 @@ int xen_cpuhp_setup(int (*cpu_up_prepare_cb)(unsigned int),
return rc >= 0 ? 0 : rc;
}
-static void xen_vcpu_setup_restore(int cpu)
+static int xen_vcpu_setup_restore(int cpu)
{
+ int rc = 0;
+
/* Any per_cpu(xen_vcpu) is stale, so reset it */
xen_vcpu_info_reset(cpu);
@@ -117,8 +119,10 @@ static void xen_vcpu_setup_restore(int cpu)
*/
if (xen_pv_domain() ||
(xen_hvm_domain() && cpu_online(cpu))) {
- xen_vcpu_setup(cpu);
+ rc = xen_vcpu_setup(cpu);
}
+
+ return rc;
}
/*
@@ -128,7 +132,7 @@ static void xen_vcpu_setup_restore(int cpu)
*/
void xen_vcpu_restore(void)
{
- int cpu;
+ int cpu, rc;
for_each_possible_cpu(cpu) {
bool other_cpu = (cpu != smp_processor_id());
@@ -148,22 +152,25 @@ void xen_vcpu_restore(void)
if (xen_pv_domain() || xen_feature(XENFEAT_hvm_safe_pvclock))
xen_setup_runstate_info(cpu);
- xen_vcpu_setup_restore(cpu);
-
- if (other_cpu && is_up &&
+ rc = xen_vcpu_setup_restore(cpu);
+ if (rc)
+ pr_emerg_once("vcpu restore failed for cpu=%d err=%d. "
+ "System will hang.\n", cpu, rc);
+ /*
+ * In case xen_vcpu_setup_restore() fails, do not bring up the
+ * VCPU. This helps us avoid the resulting OOPS when the VCPU
+ * accesses pvclock_vcpu_time via xen_vcpu (which is NULL.)
+ * Note that this does not improve the situation much -- now the
+ * VM hangs instead of OOPSing -- with the VCPUs that did not
+ * fail, spinning in stop_machine(), waiting for the failed
+ * VCPUs to come up.
+ */
+ if (other_cpu && is_up && (rc == 0) &&
HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL))
BUG();
}
}
-static void clamp_max_cpus(void)
-{
-#ifdef CONFIG_SMP
- if (setup_max_cpus > MAX_VIRT_CPUS)
- setup_max_cpus = MAX_VIRT_CPUS;
-#endif
-}
-
void xen_vcpu_info_reset(int cpu)
{
if (xen_vcpu_nr(cpu) < MAX_VIRT_CPUS) {
@@ -175,7 +182,7 @@ void xen_vcpu_info_reset(int cpu)
}
}
-void xen_vcpu_setup(int cpu)
+int xen_vcpu_setup(int cpu)
{
struct vcpu_register_vcpu_info info;
int err;
@@ -196,7 +203,7 @@ void xen_vcpu_setup(int cpu)
*/
if (xen_hvm_domain()) {
if (per_cpu(xen_vcpu, cpu) == &per_cpu(xen_vcpu_info, cpu))
- return;
+ return 0;
}
if (xen_have_vcpu_info_placement) {
@@ -230,11 +237,10 @@ void xen_vcpu_setup(int cpu)
}
}
- if (!xen_have_vcpu_info_placement) {
- if (cpu >= MAX_VIRT_CPUS)
- clamp_max_cpus();
+ if (!xen_have_vcpu_info_placement)
xen_vcpu_info_reset(cpu);
- }
+
+ return ((per_cpu(xen_vcpu, cpu) == NULL) ? -ENODEV : 0);
}
void xen_reboot(int reason)
diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
index ba1afadb2512..13b5fa1a211c 100644
--- a/arch/x86/xen/enlighten_hvm.c
+++ b/arch/x86/xen/enlighten_hvm.c
@@ -89,7 +89,7 @@ static void xen_hvm_crash_shutdown(struct pt_regs *regs)
static int xen_cpu_up_prepare_hvm(unsigned int cpu)
{
- int rc;
+ int rc = 0;
/*
* This can happen if CPU was offlined earlier and
@@ -104,7 +104,9 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
per_cpu(xen_vcpu_id, cpu) = cpu_acpi_id(cpu);
else
per_cpu(xen_vcpu_id, cpu) = cpu;
- xen_vcpu_setup(cpu);
+ rc = xen_vcpu_setup(cpu);
+ if (rc)
+ return rc;
if (xen_have_vector_callback && xen_feature(XENFEAT_hvm_safe_pvclock))
xen_setup_timer(cpu);
@@ -113,9 +115,8 @@ static int xen_cpu_up_prepare_hvm(unsigned int cpu)
if (rc) {
WARN(1, "xen_smp_intr_init() for CPU %d failed: %d\n",
cpu, rc);
- return rc;
}
- return 0;
+ return rc;
}
static int xen_cpu_dead_hvm(unsigned int cpu)
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 29cad193db53..e6639da11e0b 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -965,7 +965,16 @@ void __ref xen_setup_vcpu_info_placement(void)
for_each_possible_cpu(cpu) {
/* Set up direct vCPU id mapping for PV guests. */
per_cpu(xen_vcpu_id, cpu) = cpu;
- xen_vcpu_setup(cpu);
+
+ /*
+ * xen_vcpu_setup(cpu) can fail -- in which case it
+ * falls back to the shared_info version for cpus
+ * where xen_vcpu_nr(cpu) < MAX_VIRT_CPUS.
+ *
+ * xen_cpu_up_prepare_pv() handles the rest by failing
+ * them in hotplug.
+ */
+ (void) xen_vcpu_setup(cpu);
}
/*
@@ -1439,6 +1448,9 @@ static int xen_cpu_up_prepare_pv(unsigned int cpu)
{
int rc;
+ if (per_cpu(xen_vcpu, cpu) == NULL)
+ return -ENODEV;
+
xen_setup_timer(cpu);
rc = xen_smp_intr_init(cpu);
diff --git a/arch/x86/xen/xen-ops.h b/arch/x86/xen/xen-ops.h
index 90828256248b..0d5004477db6 100644
--- a/arch/x86/xen/xen-ops.h
+++ b/arch/x86/xen/xen-ops.h
@@ -78,7 +78,7 @@ bool xen_vcpu_stolen(int vcpu);
extern int xen_have_vcpu_info_placement;
-void xen_vcpu_setup(int cpu);
+int xen_vcpu_setup(int cpu);
void xen_vcpu_info_reset(int cpu);
void xen_setup_vcpu_info_placement(void);
--
2.7.4