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

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


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


Julien Grall



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