coverletter explanation as sent to kernel-team list:

In bionic, all archs provided by Ubuntu either define __NR_pkey_mprotect        
                                                                                
                                                                                
                               
(arm/x86) or define __IGNORE_pkey_mprotect (powerpc/s390).  This value was      
                                                                                
                                                                                
                               
used, until libseccomp was updated via bug 1815415, to instead (if              
                                                                                
                                                                                
                               
__NR_pkey_mprotect was not defined by the kernel headers) define it as a        
                                                                                
                                                                                
                               
negative error value:                                                           
                                                                                
                                                                                
                               
                                                                                
                                                                                
                                                                                
                               
+#define __PNR_pkey_mprotect    -10201                                          
                                                                                
                                                                                
                               
+#ifndef __NR_pkey_mprotect                                                     
                                                                                
                                                                                
                               
+#define __NR_pkey_mprotect     __PNR_pkey_mprotect                             
                                                                                
                                                                                
                               
+#endif /* __NR_pkey_mprotect */                                                
                                                                                
                                                                                
                               
                                                                                
                                                                                
                                                                                
                               
systemd, the next time it was built against libseccomp, pulled that             
                                                                                
                                                                                
                               
__NR_pkey_mprotect value and started using it for ppc64el, though it was        
                                                                                
                                                                                
                               
a negative error value, so it would not actually work as a syscall number.      
                                                                                
                                                                                
                               
This caused the systemd test-seccomp autopkgtest to start failing, as           
                                                                                
                                                                                
                               
the systemd function it tested only issued the pkey_mprotect syscall if         
                                                                                
                                                                                
                               
__NR_pkey_mprotect was defined.                                                 
                                                                                
                                                                                
                               
                                                                                
                                                                                
                                                                                
                               
After these patches are applied to bionic, both libseccomp and systemd will     
                                                                                
                                                                                
                               
need to be rebuilt - libseccomp rebuilt against the kernel headers, and         
                                                                                
                                                                                
                               
systemd against the libseccomp headers.                                         
                                                                                
                                                                                
                               
                                                                                
                                                                                
                                                                                
                               
Note this is not only a fix to allow a test to pass, this actually              
                                                                                
                                                                                
                               
provides the syscall number for the functionality on ppc64el on bionic,         
                                                                                
                                                                                
                               
which would have failed before (on ppc64el on bionic, but not x86/arm           
                                                                                
                                                                                
                               
on bionic); specifically one example is the systemd usage                       
                                                                                
                                                                                
                               
MemoryDenyWriteExecution as shown in bug 1725348.                               
                                                                                
                                                                                
                               
                                                                                
                                                                                
                                                                                
                               
Also note that s390x also defines __IGNORE_pkey_mprotect, but the systemd       
                                                                                
                                                                                
                               
test only expects its test case to pass for select archs, and s390x is not      
                                                                                
                                                                                
                               
one of them, so it has always expected a failure there.  It appears s390x       
                                                                                
                                                                                
                               
still does not support pkey_mprotect (it defined pkey_* starting at             
                                                                                
                                                                                
                               
commit b41c51c8e194c0bdfb4b1778a137aea8246c86cd, but appears to still           
                                                                                
                                                                                
                               
not support them).

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Packages, which is subscribed to linux in Ubuntu.
https://bugs.launchpad.net/bugs/1821625

Title:
  systemd 237-3ubuntu10.14 ADT test failure on Bionic ppc64el (test-
  seccomp)

Status in libseccomp package in Ubuntu:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Invalid
Status in libseccomp source package in Bionic:
  New
Status in linux source package in Bionic:
  New
Status in systemd source package in Bionic:
  Invalid

Bug description:
  Starting with systemd 237-3ubuntu10.14, the testcase test-seccomp is
  failing on Bionic on ppc64el with the error messages:

  Operating on architecture: ppc
  Failed to add n/a() rule for architecture ppc, skipping: Bad address
  Operating on architecture: ppc64
  Failed to add n/a() rule for architecture ppc64, skipping: Bad address
  Operating on architecture: ppc64-le
  Failed to add n/a() rule for architecture ppc64-le, skipping: Numerical 
argument out of domain
  Assertion 'p == MAP_FAILED' failed at ../src/test/test-seccomp.c:413, 
function test_memory_deny_write_execute_mmap(). Aborting.
  memoryseccomp-mmap terminated by signal ABRT.
  Assertion 'wait_for_terminate_and_check("memoryseccomp-mmap", pid, WAIT_LOG) 
== EXIT_SUCCESS' failed at ../src/test/test-seccomp.c:427, function 
test_memory_deny_write_execute_mmap(). Aborting.
  Aborted (core dumped)
  FAIL: test-seccomp (code: 134)

  Full logs at:
  
https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-bionic/bionic/ppc64el/s/systemd/20190302_025135_d0e38@/log.gz

  The testcase passed with systemd version 237-3ubuntu10.13 running on the same 
4.15.0-45 kernel on ppc64el:
  
https://objectstorage.prodstack4-5.canonical.com/v1/AUTH_77e2ada1e7a84929a74ba3b87153c0ac/autopkgtest-bionic/bionic/ppc64el/s/systemd/20190228_154406_6b12f@/log.gz

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