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

[Oleksandr <olekstysh@gmail.com>]

On 08.01.21 19:01, Jan Beulich wrote:

Hi Jan

> On 08.01.2021 17:38, Oleksandr wrote:
>> On 05.01.21 10:48, Jan Beulich wrote:
>>> On 04.01.2021 17:57, Oleksandr Tyshchenko wrote:
>>>> Hello all.
>>>>
>>>> [Sorry for the possible format issues]
>>>>
>>>> On Tue, Dec 22, 2020 at 12:41 PM Andrew Cooper <andrew.cooper3@citrix.com>
>>>> wrote:
>>>>
>>>>> On 21/12/2020 08:10, Jan Beulich wrote:
>>>>>> 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.
>>>>> Yeah, this is probably neater than the ifdefary.  My ack stands.
>>>>>
>>>>> ~Andrew
>>>>>
>>>> I might miss something or did incorrect tests, but ...
>>>> ... trying to build current staging
>>>> (7ba2ab495be54f608cb47440e1497b2795bd301a) for x86 (with # CONFIG_HVM is
>>>> not set) I got the following:
>>>>
>>>> /media/b/build/build/tmp/work/x86_64-xt-linux/domd-image-weston/1.0-r0/repo/build/tmp/work/aarch64-poky-linux/xen/4.14.0+gitAUTOINC+2c6e5a8ceb-r0/git/xen/common/memory.c:941:
>>>> undefined reference to `xenmem_add_to_physmap_one'
>>>> /media/b/build/build/tmp/work/x86_64-xt-linux/domd-image-weston/1.0-r0/repo/build/tmp/work/aarch64-poky-linux/xen/4.14.0+gitAUTOINC+2c6e5a8ceb-r0/git/xen/common/memory.c:941:(.text+0x1e391):
>>>> relocation truncated to fit: R_X86_64_PC32 against undefined symbol
>>>> `xenmem_add_to_physmap_one'
>>>> ld:
>>>> /media/b/build/build/tmp/work/x86_64-xt-linux/domd-image-weston/1.0-r0/repo/build/tmp/work/aarch64-poky-linux/xen/4.14.0+gitAUTOINC+2c6e5a8ceb-r0/git/xen/.xen-syms.0:
>>>> hidden symbol `xenmem_add_to_physmap_one' isn't defined
>>>> ld: final link failed: Bad value
>>>>
>>>> It is worth mentioning that I do not use pvshim_defconfig (I disable HVM
>>>> support via menuconfig manually before building).
>>> The specific .config may matter. The specific compiler version may
>>> also matter. Things work fine for me, both for the shim config and
>>> a custom !HVM one, with gcc10.
>> ok, after updating my a little bit ancient compiler to the latest
>> possible (?) on xenial gcc-9 the build issue had gone away. Sorry for
>> the noise.
> There's no reason to be sorry - we want Xen to build with a wide
> range of compiler versions. It's just that if a build issue is
> version dependent, it is often up to the person running into it
> to determine how to address the issue (and submit a patch).

ok, the issue was observed with gcc (Ubuntu 5.4.0-6ubuntu1~16.04.12) 
5.4.0 20160609

I think (but not 100% sure), to address the build issue something like 
the stub below could help:


diff --git a/xen/include/xen/mm.h b/xen/include/xen/mm.h
index 85a8df9..ed35352 100644
--- a/xen/include/xen/mm.h
+++ b/xen/include/xen/mm.h
@@ -609,9 +609,19 @@ union add_to_physmap_extra {
      domid_t foreign_domid;
  };

+#ifdef CONFIG_HVM
  int xenmem_add_to_physmap_one(struct domain *d, unsigned int space,
                                union add_to_physmap_extra extra,
                                unsigned long idx, gfn_t gfn);
+#else
+static inline int xenmem_add_to_physmap_one(struct domain *d,
+                                            unsigned int space,
+                                            union add_to_physmap_extra 
extra,
+                                            unsigned long idx, gfn_t gfn)
+{
+    return -EACCES;
+}
+#endif

  int xenmem_add_to_physmap(struct domain *d, struct xen_add_to_physmap 
*xatp,
                            unsigned int start);

-- 
Regards,

Oleksandr Tyshchenko