Re: [Qemu-devel] [PATCH v2] configure: enable --s390-pgste linker option

[David Hildenbrand <david@redhat.com>]

On 23.08.2017 08:53, 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.ehrhardt@canonical.com>
> Cc: Alexander Graf <agraf@suse.de>
> Cc: Dan Horak <dhorak@redhat.com>
> Cc: David Hildenbrand <david@redhat.com>
> Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
> Acked-by: Janosch Frank <frankja@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
>  }
>  
> +

I'd drop this new line

> +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 $flag ; then
>              LDFLAGS="-Wl,$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

Wonder if the "$ARCH" check is really necessary: TARGET_ARCH=s390x with
kvm=yes should only build on s390x.

> +    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
>  
> 

With the typo fixed

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David