[PATCH] xen/smp: Support NULL IPI function pointers

[Andrew Cooper <andrew.cooper3@citrix.com>]

There are several cases where the act of interrupting a remote processor has
the required side effect.  Explicitly allow NULL function pointers so the
calling code doesn't have to provide a stub implementation.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Wei Liu <wl@xen.org>

The wait parameter is a little weird.  It serves double duty and will confirm
that the IPI has been taken.  All it does is let you control whether you also
wait for the handler to complete first.  As such, it is effectively useless
with a stub function.

I don't particularly like folding into the .wait() path like that, but I
dislike it less than an if()/else if() and adding a 3rd cpumask_clear_cpu()
into the confusion which is this logic.
---
 xen/arch/x86/mm/hap/hap.c | 11 +----------
 xen/arch/x86/mm/p2m-ept.c | 11 ++---------
 xen/common/smp.c          |  4 ++++
 3 files changed, 7 insertions(+), 19 deletions(-)

diff --git a/xen/arch/x86/mm/hap/hap.c b/xen/arch/x86/mm/hap/hap.c
index 73575deb0d8a..5b269ef8b3bb 100644
--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -696,15 +696,6 @@ static void hap_update_cr3(struct vcpu *v, int do_locking, bool noflush)
     hvm_update_guest_cr3(v, noflush);
 }
 
-/*
- * Dummy function to use with on_selected_cpus in order to trigger a vmexit on
- * selected pCPUs. When the VM resumes execution it will get a new ASID/VPID
- * and thus a clean TLB.
- */
-static void dummy_flush(void *data)
-{
-}
-
 static bool flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
                       void *ctxt)
 {
@@ -737,7 +728,7 @@ static bool flush_tlb(bool (*flush_vcpu)(void *ctxt, struct vcpu *v),
      * not currently running will already be flushed when scheduled because of
      * the ASID tickle done in the loop above.
      */
-    on_selected_cpus(mask, dummy_flush, NULL, 0);
+    on_selected_cpus(mask, NULL, NULL, 0);
 
     return true;
 }
diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
index b2d57a3ee89a..1459f66c006b 100644
--- a/xen/arch/x86/mm/p2m-ept.c
+++ b/xen/arch/x86/mm/p2m-ept.c
@@ -1236,14 +1236,6 @@ static void ept_memory_type_changed(struct p2m_domain *p2m)
         ept_sync_domain(p2m);
 }
 
-static void __ept_sync_domain(void *info)
-{
-    /*
-     * The invalidation will be done before VMENTER (see
-     * vmx_vmenter_helper()).
-     */
-}
-
 static void ept_sync_domain_prepare(struct p2m_domain *p2m)
 {
     struct domain *d = p2m->domain;
@@ -1269,7 +1261,8 @@ static void ept_sync_domain_prepare(struct p2m_domain *p2m)
 
 static void ept_sync_domain_mask(struct p2m_domain *p2m, const cpumask_t *mask)
 {
-    on_selected_cpus(mask, __ept_sync_domain, p2m, 1);
+    /* Invalidation will be done in vmx_vmenter_helper(). */
+    on_selected_cpus(mask, NULL, NULL, 1);
 }
 
 void ept_sync_domain(struct p2m_domain *p2m)
diff --git a/xen/common/smp.c b/xen/common/smp.c
index 79f4ebd14502..854ebb91a803 100644
--- a/xen/common/smp.c
+++ b/xen/common/smp.c
@@ -87,10 +87,14 @@ void smp_call_function_interrupt(void)
 
     irq_enter();
 
+    if ( unlikely(!func) )
+        goto no_func;
+
     if ( call_data.wait )
     {
         (*func)(info);
         smp_mb();
+    no_func:
         cpumask_clear_cpu(cpu, &call_data.selected);
     }
     else
-- 
2.11.0