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

From: Heiko Carstens <hca@linux.ibm.com>
To: David Hildenbrand <david@redhat.com>
Cc: Thomas Huth <thuth@redhat.com>,
	Janosch Frank <frankja@linux.ibm.com>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	Cornelia Huck <cohuck@redhat.com>,
	qemu-devel@nongnu.org, Halil Pasic <pasic@linux.ibm.com>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	qemu-s390x@nongnu.org, Claudio Imbrenda <imbrenda@linux.ibm.com>,
	Richard Henderson <rth@twiddle.net>
Subject: Re: [PATCH RFC 2/5] s390x: implement diag260
Date: Wed, 15 Jul 2020 13:34:26 +0200	[thread overview]
Message-ID: <20200715113426.GD6927@osiris> (raw)
In-Reply-To: <3c163740-6299-a3dd-8b4d-58a5be123b0e@redhat.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?