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

[Jan Beulich <jbeulich@xxxxxxxx>]

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@xxxxxxxxxx>
> 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@xxxxxxxx>
>>>> Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> 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.

Jan