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

[Heiko Carstens <hca@linux.ibm.com>]

On Wed, Jul 15, 2020 at 01:21:06PM +0200, David Hildenbrand wrote:
> > At least in v4.1 the kernel will calculate the max address by using
> > increment size * increment number and then test if *each* increment is
> > available with tprot.
> 
> Yes, we do the same in kvm-unit-tests. But it's not sufficient for
> memory devices.
> 
> Just because a tprot succeed (for memory belonging to a memory device)
> does not mean the kernel should silently start to use that memory.
> 
> Note: memory devices are not just DIMMs that can be mapped to storage
> increments. The memory might have completely different semantics, that's
> why they are glued to a managing virtio device.
> 
> For example: a tprot might succeed on a memory region provided by
> virtio-mem, this does, however, not mean that the memory can (and
> should) be used by the guest.

So, are you saying that even at IPL time there might already be memory
devices attached to the system? And the kernel should _not_ treat them
as normal memory?