Re: [PATCH V2 02/23] xen/ioreq: Make x86's IOREQ feature common

[Oleksandr <olekstysh@gmail.com>]

Hi Paul

>
>> The 'legacy' mechanism of mapping magic pages for ioreq servers 
>> should remain x86 specific I think that aspect of the code needs to 
>> remain behind and not get moved into common code. You could do that 
>> in arch specific calls in hvm_ioreq_server_enable/disable() and 
>> hvm_get_ioreq_server_info().
> Well, if legacy mechanism is not going to be used for other arch and 
> should remain x86 specific, I will try to investigate what should be 
> left in x86 code and rework the series.
> As a side note, I am afraid, we won't get a 100% code movement (which 
> I managed to achieve here) for the next version of this patch as we 
> need arch/x86/hvm/ioreq.c.

I am investigating how to split the code in order to leave the 'legacy' 
mechanism x86 specific and have a few questions. Could you please 
clarify the following:

1. The split of hvm_ioreq_server_enable/disable() is obvious to me, I 
would like to clarify regarding hvm_get_ioreq_server_info().
Is it close to what you had in mind when suggesting the split of 
hvm_get_ioreq_server_info() or I just need to abstract 
hvm_ioreq_server_map_pages() call only?
(Not completed and non tested)

+/* Called with ioreq_server lock held */
+int arch_ioreq_server_get_info(struct hvm_ioreq_server *s,
+                               unsigned long *ioreq_gfn,
+                               unsigned long *bufioreq_gfn,
+                               evtchn_port_t *bufioreq_port)
+{
+    if ( ioreq_gfn || bufioreq_gfn )
+    {
+        int rc = hvm_ioreq_server_map_pages(s);
+
+        if ( rc )
+            return rc;
+    }
+
+    if ( ioreq_gfn )
+        *ioreq_gfn = gfn_x(s->ioreq.gfn);
+
+    if ( HANDLE_BUFIOREQ(s) )
+    {
+        if ( bufioreq_gfn )
+            *bufioreq_gfn = gfn_x(s->bufioreq.gfn);
+
+        if ( bufioreq_port )
+            *bufioreq_port = s->bufioreq_evtchn;
+    }
+
+    return 0;
+}
+
  int hvm_get_ioreq_server_info(struct domain *d, ioservid_t id,
                                unsigned long *ioreq_gfn,
                                unsigned long *bufioreq_gfn,
@@ -916,26 +954,7 @@ int hvm_get_ioreq_server_info(struct domain *d, 
ioservid_t id,
      if ( s->emulator != current->domain )
          goto out;

-    if ( ioreq_gfn || bufioreq_gfn )
-    {
-        rc = hvm_ioreq_server_map_pages(s);
-        if ( rc )
-            goto out;
-    }
-
-    if ( ioreq_gfn )
-        *ioreq_gfn = gfn_x(s->ioreq.gfn);
-
-    if ( HANDLE_BUFIOREQ(s) )
-    {
-        if ( bufioreq_gfn )
-            *bufioreq_gfn = gfn_x(s->bufioreq.gfn);
-
-        if ( bufioreq_port )
-            *bufioreq_port = s->bufioreq_evtchn;
-    }
-
-    rc = 0;
+    rc = arch_ioreq_server_get_info(s, ioreq_gfn, bufioreq_gfn, 
bufioreq_port);

   out:
      spin_unlock_recursive(&d->arch.hvm.ioreq_server.lock);

2. If I understand the code correctly, besides of the above-mentioned 
functions the arch specific calls should be in hvm_ioreq_server_init() 
and hvm_ioreq_server_deinit() to actually hide 
"hvm_ioreq_server_unmap_pages" usage from the common code.  I noticed 
that the rollback code in hvm_ioreq_server_init() and the whole 
hvm_ioreq_server_deinit() have a lot in common except an extra ASSERT() 
and hvm_ioreq_server_free_pages() call in the latter. My question is 
could we just replace the rollback code by hvm_ioreq_server_deinit()? I 
assume an extra hvm_ioreq_server_free_pages() call wouldn't be an issue 
here, but I am not sure what to do with the ASSERT, I expect it to be 
triggered at such an early stage (so it probably needs moving out of the 
hvm_ioreq_server_deinit() (or dropped?) as well as comment needs 
updating). I am asking, because this way we would get *a single* arch 
hook here which would be arch_ioreq_server_deinit() and remove code 
duplication a bit.

Something close to this.
(Not completed and non tested)

@@ -761,18 +771,17 @@ static int hvm_ioreq_server_init(struct 
hvm_ioreq_server *s,
      return 0;

   fail_add:
-    hvm_ioreq_server_remove_all_vcpus(s);
-    hvm_ioreq_server_unmap_pages(s);
-
-    hvm_ioreq_server_free_rangesets(s);
-
-    put_domain(s->emulator);
+    hvm_ioreq_server_deinit(s);
      return rc;
  }

+void arch_ioreq_server_deinit(struct hvm_ioreq_server *s)
+{
+    hvm_ioreq_server_unmap_pages(s);
+}
+
  static void hvm_ioreq_server_deinit(struct hvm_ioreq_server *s)
  {
-    ASSERT(!s->enabled);
      hvm_ioreq_server_remove_all_vcpus(s);

      /*
@@ -784,7 +793,7 @@ static void hvm_ioreq_server_deinit(struct 
hvm_ioreq_server *s)
       *       the page_info pointer to NULL, meaning the latter will do
       *       nothing.
       */
-    hvm_ioreq_server_unmap_pages(s);
+    arch_ioreq_server_deinit(s);
      hvm_ioreq_server_free_pages(s);

      hvm_ioreq_server_free_rangesets(s);

      put_domain(s->emulator);


-- 

Regards,

Oleksandr Tyshchenko