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

[Oleksandr <olekstysh@xxxxxxxxx>]

On 11.01.21 09:41, Jan Beulich wrote:

Hi Jan


> On 08.01.2021 18:37, Oleksandr wrote:
> > 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@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.
> > > > 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:
> I'm sure this would help, but personally I'd prefer if we could limit
> the number of such stubs and rely on the compiler DCE-ing the calls.
> Hence it would be at least desirable (imo necessary) to understand
> what prevents this to happen here, with this gcc version.
Sounds reasonable


> If you could also provide your exact .config, I could see whether I
> can repro here with some of the gcc5 versions I have laying around.
Please see attached

--
Regards,

Oleksandr Tyshchenko

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