On 08/23/2017 08:53 AM, Christian Borntraeger wrote:
> 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
>
> configure | 21 ++++++++++++++++++++-
> 1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/configure b/configure
> index dd73cce..0b68b37 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_had $flag ; then
typo, will fix with v3 :-/
> LDFLAGS="-Wl,$flag $LDFLAGS"
> fi
> done
> @@ -6522,6 +6527,20 @@ if test "$target_linux_user" = "yes" -o
> "$target_bsd_user" = "yes" ; then
> ldflags="$ldflags $textseg_ldflags"
> fi
>
> +# Newer kernels on s390 check for an S390_PGSTE program header and
> +# enable the pgste page table extensions in that case. This makes
> +# the vm.allocate_pgste sysctl unnecessary. We enable this program
> +# header if
> +# - we build on s390x
> +# - we build the system emulation for s390x (qemu-system-s390x)
> +# - KVM is enabled
> +# - the linker support --s390-pgste
> +if test "$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
>
