Re: [PATCH RFC 2/5] s390x: implement diag260

[David Hildenbrand]

On 10.07.20 17:18, Heiko Carstens wrote:
> On Fri, Jul 10, 2020 at 02:12:33PM +0200, David Hildenbrand wrote:
>>> Note: Reading about diag260 subcode 0xc, we could modify Linux to query
>>> the maximum possible pfn via diag260 0xc. Then, we maybe could avoid
>>> indicating maxram size via SCLP, and keep diag260-unaware OSs keep
>>> working as before. Thoughts?
>>
>> Implemented it, seems to work fine.
> 
> The returned value would not include standby/reserved memory within
> z/VM. So this seems not to work.

Which value exactly are you referencing? diag 0xc returns two values.
One of them seems to do exactly what we need.

See
https://github.com/davidhildenbrand/linux/commit/a235f9fb20df7c04ae89bc0d134332d1a01842c7

for my current Linux approach.

> Also: why do you want to change this

Which change exactly do you mean?

If we limit the value returned via SCLP to initial memory, we cannot
break any guest (e.g., Linux pre 4.2, kvm-unit-tests). diag260 is then
purely optional.

-- 
Thanks,

David / dhildenb