Re: [qemu-s390x] [Qemu-devel] [PATCH v2 2/2] s390x: Enable KVM huge page backing support

[Thomas Huth]

On 07/31/2018 11:09 AM, Janosch Frank wrote:
> QEMU has had huge page support for a longer time already, but KVM
> memory management under s390x needed some changes to work with huge
> backings.
> 
> Now that we have support, let's enable it if requested and
> available. Otherwise we now properly tell the user if there is no
> support and back out instead of failing to run the VM later on.
> 
> Signed-off-by: Janosch Frank <address@hidden>
> ---
>  target/s390x/kvm.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index d923cf4240..26e6937498 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -285,6 +285,12 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>  {
>      MachineClass *mc = MACHINE_GET_CLASS(ms);
>  
> +    if (mem_path && kvm_vm_enable_cap(s, KVM_CAP_S390_HPAGE, 0)) {
> +        error_report("Huge page backing was specified, "
> +                     "but this KVM does not support huge pages");
> +        return -EINVAL;
> +    }

I think you should also check the page size of the mem_path (e.g. with
qemu_mempath_getpagesize() ?), since a mem_path does not automatically
mean huge pages, does it?

 Thomas


PS: Please CC: address@hidden for s390x patches!