[PATCH v4 5/5] x86/xen: Fix xen_hvm_smp_init() when vector callback not available

[David Woodhouse <dwmw2@xxxxxxxxxxxxx>]

From: David Woodhouse <dwmw@xxxxxxxxxxxx>

Only the IPI-related functions in the smp_ops should be conditional
on the vector callback being available. The rest should still happen:

 • xen_hvm_smp_prepare_boot_cpu()

   This function does two things, both of which should still happen if
   there is no vector callback support.

   The call to xen_vcpu_setup() for vCPU0 should still happen as it just
   sets up the vcpu_info for CPU0. That does happen for the secondary
   vCPUs too, from xen_cpu_up_prepare_hvm().

   The second thing it does is call xen_init_spinlocks(), which perhaps
   counter-intuitively should *also* still be happening in the case
   without vector callbacks, so that it can clear its local xen_pvspin
   flag and disable the virt_spin_lock_key accordingly.

   Checking xen_have_vector_callback in xen_init_spinlocks() itself
   would affect PV guests, so set the global nopvspin flag in
   xen_hvm_smp_init() instead, when vector callbacks aren't available.

 • xen_hvm_smp_prepare_cpus()

   This does some IPI-related setup by calling xen_smp_intr_init() and
   xen_init_lock_cpu(), which can be made conditional. And it sets the
   xen_vcpu_id to XEN_VCPU_ID_INVALID for all possible CPUS, which does
   need to happen.

 • xen_smp_cpus_done()

   This offlines any vCPUs which doesn't fit in the global shared_info
   page, if separate vcpu_info placement isn't available. That part also
   needs to happen regardless of vector callback support.

 • xen_hvm_cpu_die()

   This doesn't actually do anything other than commin_cpu_die() right
   right now in the !vector_callback case; all three teardown functions
   it calls should be no-ops. But to guard against future regressions
   it's useful to call it anyway, and for it to explicitly check for
   xen_have_vector_callback before calling those additional functions.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 arch/x86/xen/smp_hvm.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/arch/x86/xen/smp_hvm.c b/arch/x86/xen/smp_hvm.c
index f5e7db4f82ab..056430a1080b 100644
--- a/arch/x86/xen/smp_hvm.c
+++ b/arch/x86/xen/smp_hvm.c
@@ -33,9 +33,11 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int 
max_cpus)
        int cpu;
 
        native_smp_prepare_cpus(max_cpus);
-       WARN_ON(xen_smp_intr_init(0));
 
-       xen_init_lock_cpu(0);
+       if (xen_have_vector_callback) {
+               WARN_ON(xen_smp_intr_init(0));
+               xen_init_lock_cpu(0);
+       }
 
        for_each_possible_cpu(cpu) {
                if (cpu == 0)
@@ -50,9 +52,11 @@ static void __init xen_hvm_smp_prepare_cpus(unsigned int 
max_cpus)
 static void xen_hvm_cpu_die(unsigned int cpu)
 {
        if (common_cpu_die(cpu) == 0) {
-               xen_smp_intr_free(cpu);
-               xen_uninit_lock_cpu(cpu);
-               xen_teardown_timer(cpu);
+               if (xen_have_vector_callback) {
+                       xen_smp_intr_free(cpu);
+                       xen_uninit_lock_cpu(cpu);
+                       xen_teardown_timer(cpu);
+               }
        }
 }
 #else
@@ -64,14 +68,17 @@ static void xen_hvm_cpu_die(unsigned int cpu)
 
 void __init xen_hvm_smp_init(void)
 {
-       if (!xen_have_vector_callback)
+       smp_ops.smp_prepare_boot_cpu = xen_hvm_smp_prepare_boot_cpu;
+       smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
+       smp_ops.smp_cpus_done = xen_smp_cpus_done;
+       smp_ops.cpu_die = xen_hvm_cpu_die;
+
+       if (!xen_have_vector_callback) {
+               nopvspin = true;
                return;
+       }
 
-       smp_ops.smp_prepare_cpus = xen_hvm_smp_prepare_cpus;
        smp_ops.smp_send_reschedule = xen_smp_send_reschedule;
-       smp_ops.cpu_die = xen_hvm_cpu_die;
        smp_ops.send_call_func_ipi = xen_smp_send_call_function_ipi;
        smp_ops.send_call_func_single_ipi = 
xen_smp_send_call_function_single_ipi;
-       smp_ops.smp_prepare_boot_cpu = xen_hvm_smp_prepare_boot_cpu;
-       smp_ops.smp_cpus_done = xen_smp_cpus_done;
 }
-- 
2.29.2