Re: [PATCH 2/6] x86/mm: p2m_add_foreign() is HVM-only

[Jan Beulich <jbeulich@suse.com>]

On 17.12.2020 20:18, Andrew Cooper wrote:
> On 15/12/2020 16:26, Jan Beulich wrote:
>> This is together with its only caller, xenmem_add_to_physmap_one().
> 
> I can't parse this sentence.  Perhaps "... as is it's only caller," as a
> follow-on from the subject sentence.
> 
>>  Move
>> the latter next to p2m_add_foreign(), allowing this one to become static
>> at the same time.
>>
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> 
> Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

So I had to ask Andrew to revert this (I was already at home when
noticing the breakage), as it turned out to break the shim build.
The problem is that xenmem_add_to_physmap() is non-static and
hence can't be eliminated altogether by the compiler when !HVM.
We could make the function conditionally static
"#if !defined(CONFIG_X86) && !defined(CONFIG_HVM)", but this
looks uglier to me than this extra hunk:

--- unstable.orig/xen/common/memory.c
+++ unstable/xen/common/memory.c
@@ -788,7 +788,11 @@ int xenmem_add_to_physmap(struct domain
     union add_to_physmap_extra extra = {};
     struct page_info *pages[16];
 
-    ASSERT(paging_mode_translate(d));
+    if ( !paging_mode_translate(d) )
+    {
+        ASSERT_UNREACHABLE();
+        return -EACCES;
+    }
 
     if ( xatp->space == XENMAPSPACE_gmfn_foreign )
         extra.foreign_domid = DOMID_INVALID;

Andrew, please let me know whether your ack stands with this (or
said alternative) added, or whether you'd prefer me to re-post.

Jan