KVM guests on s390 need a different page table layout than normal processes (2kb page table + 2kb page status extensions vs 2kb page table only). As of today this has to be enabled via the vm.allocate_pgste sysctl.
Newer kernels (>= 4.12) on s390 check for an S390_PGSTE program header and enable the pgste page table extensions in that case. This makes the vm.allocate_pgste sysctl unnecessary. We enable this program header for the s390 system emulation (qemu-system-s390x) if - the linker supports --s390-pgste (binutils >= 2.29) - KVM is enabled This will allow distributions to disable the global vm.allocate_pgste sysctl, which will improve the page table allocation for non KVM processes as only 2kb chunks are necessary. Cc: Christian Ehrhardt <christian.ehrha...@canonical.com> Cc: Alexander Graf <ag...@suse.de> Cc: Dan Horak <dho...@redhat.com> Cc: David Hildenbrand <da...@redhat.com> Signed-off-by: Christian Borntraeger <borntrae...@de.ibm.com> Acked-by: Janosch Frank <fran...@linux.vnet.ibm.com> --- configure | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/configure b/configure index dd73cce..4c9084b 100755 --- a/configure +++ b/configure @@ -6522,6 +6522,19 @@ if test "$target_linux_user" = "yes" -o "$target_bsd_user" = "yes" ; then ldflags="$ldflags $textseg_ldflags" fi +# Newer kernels on s390 check for an S390_PGSTE program header and +# enable the pgste page table extensions in that case. This makes +# the vm.allocate_pgste sysctl unnecessary. We enable this program +# header if +# - the linker support --s390-pgste +# - we build the system emulation (qemu-system-s390x) +# - KVM is enabled +if $ld --help 2>/dev/null | grep ".--s390-pgste" >/dev/null 2>/dev/null ; then + if test "$target_softmmu" = "yes" -a "$ARCH" = "s390x" -a "$kvm" = "yes" ; then + ldflags="-Wl,--s390-pgste $ldflags" + fi +fi + echo "LDFLAGS+=$ldflags" >> $config_target_mak echo "QEMU_CFLAGS+=$cflags" >> $config_target_mak -- 2.7.4
