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 we build on s390
- for s390 system emulation
- 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>
---
V1->V2:
- provide ld_has function
- use ld_has to replace some open coded variants
- check target arch and arch for s390
- check for s390x before calling the linker
V2->V3:
- fix typos
configure | 21 ++++++++++++++++++++-
1 file changed, 20 insertions(+), 1 deletion(-)
diff --git a/configure b/configure
index dd73cce..fb7e34a 100755
--- a/configure
+++ b/configure
@@ -240,6 +240,11 @@ supported_target() {
return 1
}
+
+ld_has() {
+ $ld --help 2>/dev/null | grep ".$1" >/dev/null 2>&1
+}
+
# default parameters
source_path=$(dirname "$0")
cpu=""
@@ -5043,7 +5048,7 @@ fi
# Use ASLR, no-SEH and DEP if available
if test "$mingw32" = "yes" ; then
for flag in --dynamicbase --no-seh --nxcompat; do
- if $ld --help 2>/dev/null | grep ".$flag" >/dev/null 2>/dev/null ; then
+ if ld_has $flag ; then
LDFLAGS="-Wl,$flag $LDFLAGS"
fi
done
@@ -6522,6 +6527,20 @@ if test "$target_linux_user" = "yes" -o
"$target_bsd_user" = "yes" ; then
ldflags="$ldflags $textseg_ldflags"
fi
+# Newer kernels on s390 check for an S390_PGSTE program header and
+# enable the pgste page table extensions in that case. This makes
+# the vm.allocate_pgste sysctl unnecessary. We enable this program
+# header if
+# - we build on s390x
+# - we build the system emulation for s390x (qemu-system-s390x)
+# - KVM is enabled
+# - the linker supports --s390-pgste
+if test "$TARGET_ARCH" = "s390x" -a "$target_softmmu" = "yes" -a "$ARCH" =
"s390x" -a "$kvm" = "yes"; then
+ if ld_has --s390-pgste ; then
+ ldflags="-Wl,--s390-pgste $ldflags"
+ fi
+fi
+
echo "LDFLAGS+=$ldflags" >> $config_target_mak
echo "QEMU_CFLAGS+=$cflags" >> $config_target_mak
--
2.7.4
