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

[Janosch Frank]

On 31.07.2018 15:06, Cornelia Huck wrote:
> On Tue, 31 Jul 2018 13:09:08 +0100
> Janosch Frank <address@hidden> 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)) {
> 
> 1 * MiB ?

I only looked for page size definitions, didn't know it exists, yes 1 *
MiB is a bit nicer.

I'd wait for more comments before sending the v4 out, so consider this
fixed.

> 
>> +            error_report("Huge page backing with pages > 1M was specified, "
>> +                         "but KVM does not support this memory backing");
>> +            return -EINVAL;
>> +
>> +        }
>> +        if (kvm_vm_enable_cap(s, KVM_CAP_S390_HPAGE_1M, 0)) {
>> +            error_report("Huge page backing with 1M pages was specified, "
>> +                         "but KVM does not support this memory backing");
>> +            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);
> 
>

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