On 22.08.2017 16:47, 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
> - 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
>/dev/null 2>&1
(from has(){} definiton)
maybe even introduce
ld_has() {
$ld --help 2>/dev/null | grep ".$1" >/dev/null 2>&1
}
I guess it also makes sense to test for s390x first, before checking for
ld support.
> + if test "$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
>
>
Happy to see this change :)
--
Thanks,
David
