[Xen-devel] [PATCH v2 3/3] hvm_has_dm: Do a full check for backing DM

[Don Slutz <dslutz@xxxxxxxxxxx>]

This saves a VMENTRY and a VMEXIT since we not longer retry the
ioport read on backing DM not handling a given ioreq.

To only call on hvm_select_ioreq_server() once in this code path, return s.
Also switch to hvm_send_assist_req_to_ioreq_server().

Signed-off-by: Don Slutz <dslutz@xxxxxxxxxxx>
---
v2:
  Paul Durrant:
    I think the two changes only make sense in combination.
      folded old #3 and old #5 into #3.
    Actually that comment is not right. The operation is not binned;
    it's just already been done.
      Comment has been dropped.
    I think you can ASSERT(s) here, as you should never get here ...
      Dropped call to hvm_complete_assist_req(), added ASSERT.
    So basically collapses down to just this call.
      Yes, so changed to call on hvm_send_assist_req_to_ioreq_server()
      and removed hvm_send_assist_req() which had 1 caller.

  Jan Beulich:
    The change on what to do when hvm_send_assist_req() fails is bad.
      That is correct.  Made hvm_has_dm() do full checking so
      that the extra VMEXIT and VMENTRY can be skipped.
    hvm_complete_assist_req() be a separate function yet having only
    a single caller ...
      Folded hvm_complete_assist_req() in to hvm_has_dm() which
      is the only place it is called.


 xen/arch/x86/hvm/emulate.c    |  8 ++++++--
 xen/arch/x86/hvm/hvm.c        | 25 ++++++++-----------------
 xen/include/asm-x86/hvm/hvm.h |  6 ++++--
 3 files changed, 18 insertions(+), 21 deletions(-)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 2ed4344..dca6d2e 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -218,8 +218,11 @@ static int hvmemul_do_io(
             vio->io_state = HVMIO_handle_mmio_awaiting_completion;
         break;
     case X86EMUL_UNHANDLEABLE:
+    {
+        struct hvm_ioreq_server *s = hvm_has_dm(curr->domain, &p);
+
         /* If there is no backing DM, just ignore accesses */
-        if ( !hvm_has_dm(curr->domain) )
+        if ( !s )
         {
             rc = X86EMUL_OKAY;
             vio->io_state = HVMIO_none;
@@ -227,11 +230,12 @@ static int hvmemul_do_io(
         else
         {
             rc = X86EMUL_RETRY;
-            if ( !hvm_send_assist_req(&p) )
+            if ( !hvm_send_assist_req_to_ioreq_server(s, &p) )
                 vio->io_state = HVMIO_none;
             else if ( p_data == NULL )
                 rc = X86EMUL_OKAY;
         }
+    }
         break;
     default:
         BUG();
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 6f7b407..81bdf18 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2507,11 +2507,6 @@ int hvm_buffered_io_send(ioreq_t *p)
     return 1;
 }
 
-bool_t hvm_has_dm(struct domain *d)
-{
-    return !list_empty(&d->arch.hvm_domain.ioreq_server.list);
-}
-
 bool_t hvm_send_assist_req_to_ioreq_server(struct hvm_ioreq_server *s,
                                            ioreq_t *proto_p)
 {
@@ -2519,6 +2514,7 @@ bool_t hvm_send_assist_req_to_ioreq_server(struct 
hvm_ioreq_server *s,
     struct domain *d = curr->domain;
     struct hvm_ioreq_vcpu *sv;
 
+    ASSERT(s);
     if ( unlikely(!vcpu_start_shutdown_deferral(curr)) )
         return 0; /* implicitly bins the i/o operation */
 
@@ -2571,8 +2567,13 @@ bool_t hvm_send_assist_req_to_ioreq_server(struct 
hvm_ioreq_server *s,
     return 0;
 }
 
-static bool_t hvm_complete_assist_req(ioreq_t *p)
+struct hvm_ioreq_server *hvm_has_dm(struct domain *d, ioreq_t *p)
 {
+    struct hvm_ioreq_server *s = hvm_select_ioreq_server(current->domain, p);
+
+    if ( s )
+        return s;
+
     ASSERT(p->type != IOREQ_TYPE_PCI_CONFIG);
     switch ( p->type )
     {
@@ -2599,17 +2600,7 @@ static bool_t hvm_complete_assist_req(ioreq_t *p)
         break;
     }
 
-    return 1;
-}
-
-bool_t hvm_send_assist_req(ioreq_t *p)
-{
-    struct hvm_ioreq_server *s = hvm_select_ioreq_server(current->domain, p);
-
-    if ( !s )
-        return hvm_complete_assist_req(p);
-
-    return hvm_send_assist_req_to_ioreq_server(s, p);
+    return NULL;
 }
 
 void hvm_broadcast_assist_req(ioreq_t *p)
diff --git a/xen/include/asm-x86/hvm/hvm.h b/xen/include/asm-x86/hvm/hvm.h
index e3d2d9a..4bcc61c 100644
--- a/xen/include/asm-x86/hvm/hvm.h
+++ b/xen/include/asm-x86/hvm/hvm.h
@@ -228,7 +228,9 @@ int hvm_vcpu_cacheattr_init(struct vcpu *v);
 void hvm_vcpu_cacheattr_destroy(struct vcpu *v);
 void hvm_vcpu_reset_state(struct vcpu *v, uint16_t cs, uint16_t ip);
 
-bool_t hvm_send_assist_req(ioreq_t *p);
+struct hvm_ioreq_server;
+bool_t hvm_send_assist_req_to_ioreq_server(struct hvm_ioreq_server *s,
+                                           ioreq_t *p);
 void hvm_broadcast_assist_req(ioreq_t *p);
 
 void hvm_get_guest_pat(struct vcpu *v, u64 *guest_pat);
@@ -359,7 +361,7 @@ void hvm_hypervisor_cpuid_leaf(uint32_t sub_idx,
 void hvm_cpuid(unsigned int input, unsigned int *eax, unsigned int *ebx,
                                    unsigned int *ecx, unsigned int *edx);
 void hvm_migrate_timers(struct vcpu *v);
-bool_t hvm_has_dm(struct domain *d);
+struct hvm_ioreq_server *hvm_has_dm(struct domain *d, ioreq_t *p);
 bool_t hvm_io_pending(struct vcpu *v);
 void hvm_do_resume(struct vcpu *v);
 void hvm_migrate_pirqs(struct vcpu *v);
-- 
1.8.4


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