[PATCH 5/5] x86/HVM: don't setup an intercept handler for IO port 0xcf8 unconditionally

[Roger Pau Monne <roger.pau@citrix.com>]

Only intercept accesses to IO port 0xcf8 if there's at least one IOREQ
server, otherwise it makes no sense since the only code that uses the value
stored by hvm_access_cf8 is the IOREQ server.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
---
Cc: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
---
 xen/arch/x86/hvm/hvm.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index 28c6cd9..24c3d46 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -1141,6 +1141,13 @@ static int hvm_create_ioreq_server(struct domain *d, domid_t domid,
     if ( rc )
         goto fail3;
 
+    /*
+     * We cannot fail after this point, or we risk registering the handler
+     * multiple times (there's no unregister function yet).
+     */
+    if ( list_empty(&d->arch.hvm_domain.ioreq_server.list) )
+        register_portio_handler(d, 0xcf8, 4, hvm_access_cf8);
+
     list_add(&s->list_entry,
              &d->arch.hvm_domain.ioreq_server.list);
 
@@ -1625,7 +1632,6 @@ int hvm_domain_initialise(struct domain *d)
     pit_init(d, cpu_khz);
 
     register_portio_handler(d, 0xe9, 1, hvm_print_line);
-    register_portio_handler(d, 0xcf8, 4, hvm_access_cf8);
 
     rc = hvm_funcs.domain_initialise(d);
     if ( rc != 0 )
-- 
1.9.5 (Apple Git-50.3)


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