Re: [Qemu-devel] [PATCH v3] configure: enable --s390-pgste linker option

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 23 Aug 2017 12:16:23 +0200
Christian Borntraeger <borntraeger@de.ibm.com> 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
> V2->V3: 
> 	- fix typos
>  configure | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)

Looks sane.

I guess I'll wait for some more Acks or R-bs and then queue it to
s390-next.