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

[Julien Grall <julien@xxxxxxx>]

Hi Jan & Oleksandr,

On 13/01/2021 15:06, Oleksandr wrote:
> On 12.01.21 13:58, Jan Beulich wrote:
>
> Hi Jan.
>
> > On 11.01.2021 09:23, Oleksandr wrote:
> > > On 11.01.21 09:41, Jan Beulich wrote:
> > > > 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
> > Builds perfectly fine with 5.4.0 here.
> Thank you for testing.
>
>
> I wonder whether I indeed missed something. I have switched to 5.4.0 
> again (from 9.3.0) and rechecked, a build issue was still present.
> I even downloaded 5.4.0 sources and built them to try to build Xen, and 
> got the same effect.  What I noticed is that for non-debug builds the 
> build issue wasn't present.
> Then I decided to build today's staging 
> (414be7b66349e7dca42bc1fd47c2b2f5b2d27432 xen/memory: Fix compat 
> XENMEM_acquire_resource for size requests) instead of 9-day's old one when
> I had initially reported about that build issue 
> (7ba2ab495be54f608cb47440e1497b2795bd301a x86/p2m: Fix 
> paging_gva_to_gfn() for nested virt). Today's staging builds perfectly 
> fine with 5.4.0.
> It seems that commit in the middle 
> (994f6478a48a60e3b407c7defc2d36a80f880b04 xsm/dummy: harden against 
> speculative abuse) indirectly fixes that weird build issue with 5.4.0...
The gitlab CI reported a similar issue today (see [1]) when building 
with randconfig ([2]). This is happening on Debian sid with GCC 9.3.
Note that the default compiler on sid is GCC 10.2.1. So you will have to 
install the package gcc-9 and then use CC=gcc-9 make <...>.

From a local repro, I get the following message:

ld: ld: prelink.o: in function `xenmem_add_to_physmap_batch':
/root/xen/xen/common/memory.c:942: undefined reference to 
`xenmem_add_to_physmap_one'
/root/xen/xen/common/memory.c:942:(.text+0x22145): relocation truncated 
to fit: R_X86_64_PLT32 against undefined symbol `xenmem_add_to_physmap_one'
prelink-efi.o: in function `xenmem_add_to_physmap_batch':
/root/xen/xen/common/memory.c:942: undefined reference to 
`xenmem_add_to_physmap_one'
make[2]: *** [Makefile:215: /root/xen/xen/xen.efi] Error 1
make[2]: *** Waiting for unfinished jobs....
ld: /root/xen/xen/.xen-syms.0: hidden symbol `xenmem_add_to_physmap_one' 
isn't defined
ld: final link failed: bad value


This points to the call in xenmem_add_to_physmap_batch(). I have played 
a bit with the .config options. I was able to get it built as soon as I 
disabled CONFIG_COVERAGE=y.
So maybe the optimizer is not clever enough on GCC 9 when building with 
coverage enabled?
With the diff below applied (borrowed from 
xenmem_add_to_physmap_batch()), I can build without tweaking the .config 
[1]:
diff --git a/xen/common/memory.c b/xen/common/memory.c
index ccb4d49fc6..5cfd36a53d 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -903,6 +903,12 @@ static int xenmem_add_to_physmap_batch(struct 
domain *d,
 {
     union add_to_physmap_extra extra = {};

+    if ( !paging_mode_translate(d) )
+    {
+        ASSERT_UNREACHABLE();
+        return -EACCES;
+    }
+
     if ( unlikely(xatpb->size < extent) )
         return -EILSEQ;

Cheers,

[1] https://gitlab.com/xen-project/xen/-/jobs/981624525
[2] https://pastebin.com/vTbQXXV9


https://gitlab.com/xen-project/xen/-/jobs/981624525

>
--
Julien Grall