Re: [Qemu-devel] [PATCH v3 2/2] s390x: Enable KVM huge page backing support

[Thomas Huth]

On 07/31/2018 02:09 PM, 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 | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index d923cf4240..f961c3b84a 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -34,6 +34,7 @@
>  #include "qapi/error.h"
>  #include "qemu/error-report.h"
>  #include "qemu/timer.h"
> +#include "qemu/mmap-alloc.h"
>  #include "sysemu/sysemu.h"
>  #include "sysemu/hw_accel.h"
>  #include "hw/hw.h"
> @@ -285,6 +286,20 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>  {
>      MachineClass *mc = MACHINE_GET_CLASS(ms);
>  
> +    if (mem_path) {
> +        if (qemu_mempath_getpagesize(mem_path) != (1 << 20)) {
> +            error_report("Huge page backing with pages > 1M was specified, "
> +                         "but KVM does not support this memory backing");
> +            return -EINVAL;

I think you should use ">" instead of "!=" here. It does not make much
too much sense, but it is still possible that the user specifies a
mem_path with 4k, and you don't want to trigger the error message here
(try something like qemu-system-s390x -mem-path /tmp/... for example).

 Thomas