[Qemu-devel] [PATCH v2 0/2] s390x: Enable KVM huge page backing support

[Qemu-devel] [PATCH v2 0/2] s390x: Enable KVM huge page backing support

[Janosch Frank]

Will be available with kernel 4.19.

Janosch Frank (2):
  kvm: sync linux headers
  s390x: Enable KVM huge page backing support

 linux-headers/linux/kvm.h | 1 +
 target/s390x/kvm.c        | 6 ++++++
 2 files changed, 7 insertions(+)

-- 
2.14.3

[Qemu-devel] [PATCH v2 1/2] kvm: sync linux headers

[Janosch Frank]

Import KVM_CAP_S390_HPAGE.
Placeholder for proper sync.

Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
---
 linux-headers/linux/kvm.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
index 98f389a5a3..e3b1e3070c 100644
--- a/linux-headers/linux/kvm.h
+++ b/linux-headers/linux/kvm.h
@@ -949,6 +949,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_GET_MSR_FEATURES 153
 #define KVM_CAP_HYPERV_EVENTFD 154
 #define KVM_CAP_HYPERV_TLBFLUSH 155
+#define KVM_CAP_S390_HPAGE 156
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
-- 
2.14.3

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

[Janosch Frank]

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 <frankja@linux.ibm.com>
---
 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;
+    }
+
     mc->default_cpu_type = S390_CPU_TYPE_NAME("host");
     cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS);
     cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
-- 
2.14.3

Re: [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 <frankja@linux.ibm.com>
> ---
>  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: qemu-s390x@nongnu.org for s390x patches!