Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT) to support QEMU/KVM memory devices

[Alexander Gordeev]

On Thu, Oct 17, 2024 at 02:07:12PM +0200, David Hildenbrand wrote:
> On 17.10.24 12:00, David Hildenbrand wrote:
> > Well, DIAGNOSE 260 is z/VM only and DIAG 500 is KVM only. So there are
> > currently not really any other reasonable ways besides SCLP.
> 
> Correction: Staring at the code again, in detect_physmem_online_ranges()
> we will indeed try:
> 
> a) sclp_early_read_storage_info()
> b) diag260()

So why care to call diag260() in case of DIAGNOSE 500? What about the below?

void detect_physmem_online_ranges(unsigned long max_physmem_end)
{
	if (!sclp_early_read_storage_info()) {
		physmem_info.info_source = MEM_DETECT_SCLP_STOR_INFO;
	} else if (physmem_info.info_source == MEM_DETECT_DIAG500_STOR_LIMIT) {
		unsigned long online_end;

		if (!sclp_early_get_memsize(&online_end)) {
			physmem_info.info_source = MEM_DETECT_SCLP_READ_INFO;
			add_physmem_online_range(0, online_end);
		}
	} else if (!diag260()) {
		physmem_info.info_source = MEM_DETECT_DIAG260;
	} else if (max_physmem_end) {
		add_physmem_online_range(0, max_physmem_end);
	}
}

> But if neither works, we cannot blindly add all that memory, something is
> messed up. So we'll fallback to
> 
> c) sclp_early_get_memsize()
> 
> But if none of that works, something is seriously wrong.

Ok, thanks for the clarification.