Re: [PATCH] x86/mem_sharing: Fix build folloing VM Fork work

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/04/2020 00:23, Tamas K Lengyel wrote:
> On Thu, Apr 9, 2020 at 5:00 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 
> wrote:
>> On 09/04/2020 23:38, Tamas K Lengyel wrote:
>>> On Thu, Apr 9, 2020 at 4:05 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 
>>> wrote:
>>>> On 09/04/2020 22:24, Tamas K Lengyel wrote:
>>>>> On Thu, Apr 9, 2020 at 2:48 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> 
>>>>> wrote:
>>>>>> A default build fails with:
>>>>>>
>>>>>>   mem_sharing.c: In function ‘copy_special_pages’:
>>>>>>   mem_sharing.c:1649:9: error: ‘HVM_PARAM_STORE_PFN’ undeclared (first 
>>>>>> use in this function)
>>>>>>            HVM_PARAM_STORE_PFN,
>>>>>>            ^~~~~~~~~~~~~~~~~~~
>>>>>>
>>>>>> I suspect this is a rebasing issue with respect to c/s 12f0c69f2709 
>>>>>> "x86/HVM:
>>>>>> reduce hvm.h include dependencies".
>>>>>>
>>>>>> Fixes: 41548c5472a "mem_sharing: VM forking"
>>>>>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>>>> So staging definitely compiles for me both with and without
>>>>> CONFIG_MEM_SHARING enabled. By default its off, so this shouldn't even
>>>>> be compiled so I'm curious what's happening in your build. That said,
>>>>> I have no objection to the extra include if it turns out to be
>>>>> actually necessary.
>>>> Exact config attached.  I've just double checked that staging fails.
>>>>
>>>> We should get  to the bottom of exactly what is going on here, if it
>>>> isn't the obvious thing.
>>> Strange, with your config it does produce the error. With "echo
>>> CONFIG_MEM_SHARING=y > .config && XEN_CONFIG_EXPERT=y make
>>> olddefconfig && make" it does compile.
>> You lose XEN_CONFIG_EXPERT=y in the second make, so it rewrites your
>> .config behind your back.  (This behaviour is totally obnoxious).
> I also compiled with export XEN_CONFIG_EXPERT=y and it compiles fine.
>
>> Diff the current config against original?
> drt@t0:~/workspace/xen/xen$ diff .config .config-debug
> 6c6
> < CONFIG_GCC_VERSION=80300
> ---
>> CONFIG_GCC_VERSION=60300

;-(

I occasionally forget that `diff` defaults to unreadable.

>> # CONFIG_XEN_ALIGN_DEFAULT is not set
>> CONFIG_XEN_ALIGN_2M=y
>> CONFIG_GUEST=y
>> CONFIG_XEN_GUEST=y
>> CONFIG_PVH_GUEST=y
>> CONFIG_PV_SHIM=y
>> # CONFIG_PV_SHIM_EXCLUSIVE is not set
>> CONFIG_HYPERV_GUEST=y
> 61,62c65,74
> < # CONFIG_XSM is not set

With XSM compiled out, xsm/dummy.h is used, and has to include
public/hvm/params.h to get XEN_ALTP2M_* for xsm_hvm_altp2mhvm_op(), and
this bleeds through into everything which includes xsm/xsm.h, which is
basically everything.

Are you happy for me to fix up the commit message to this effect,
replacing the previous guesswork?

~Andrew