Re: [qemu-s390x] [PATCH v4 2/2] s390x: Enable KVM huge page backing support

[Janosch Frank]

On 01.08.2018 18:47, Thomas Huth wrote:
> On 08/01/2018 03:19 PM, Janosch Frank wrote:
>> +static int kvm_s390_configure_mempath_backing(KVMState *s)
>> +{
>> +    size_t path_psize = qemu_mempath_getpagesize(mem_path);
>> +
>> +    if (path_psize == 4 * KiB)
>> +        return 0;
> 
> Missing curly braces.

urgh, right, this is not the kernel.

> 
>> +    if (path_psize != 1 * MiB) {
>> +        error_report("Memory backing with 2G pages was specified, "
>> +                     "but KVM does not support this memory backing");
> 
> May I suggest to use a text that rather matches the condition of the
> if-statement (just in case there will be other sizes in the future...),
> e.g. "Memory backing is only supported for 1 MiB huge pages" or
> something similar.
> 
>  Thomas
> 

That's actually the gist of it. s390 supports 4k, 1M and 2G and looking
at the POP I don't see a big chance of having any more sizes, as there
are not a lot of software bits left and adding support in OSs is a pain.
Also don't hold your breath for 2G, it would need a rewrite of gmap.c.

Also this is more explicit.

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