linux-kernel - [PATCH v2 3/7] Documentation: s390-diag.rst: document diag500(STORAGE LIMIT) subfunction

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Message-ID: <20241014144622.876731-4-david@redhat.com>
Date: Mon, 14 Oct 2024 16:46:15 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	linux-s390@...r.kernel.org,
	virtualization@...ts.linux.dev,
	linux-doc@...r.kernel.org,
	kvm@...r.kernel.org,
	David Hildenbrand <david@...hat.com>,
	Heiko Carstens <hca@...ux.ibm.com>,
	Vasily Gorbik <gor@...ux.ibm.com>,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Sven Schnelle <svens@...ux.ibm.com>,
	Thomas Huth <thuth@...hat.com>,
	Cornelia Huck <cohuck@...hat.com>,
	Janosch Frank <frankja@...ux.ibm.com>,
	Claudio Imbrenda <imbrenda@...ux.ibm.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jonathan Corbet <corbet@....net>
Subject: [PATCH v2 3/7] Documentation: s390-diag.rst: document diag500(STORAGE LIMIT) subfunction

Let's document our new diag500 subfunction that can be implemented by
userspace.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 Documentation/virt/kvm/s390/s390-diag.rst | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/Documentation/virt/kvm/s390/s390-diag.rst b/Documentation/virt/kvm/s390/s390-diag.rst
index d9b7c6cbc99e..c69c6e0fa71b 100644
--- a/Documentation/virt/kvm/s390/s390-diag.rst
+++ b/Documentation/virt/kvm/s390/s390-diag.rst
@@ -77,6 +77,23 @@ Subcode 3 - virtio-ccw notification
 
     See also the virtio standard for a discussion of this hypercall.
 
+Subcode 4 - storage-limit
+    Handled by userspace.
+
+    After completion of the DIAGNOSE call, general register 2 will
+    contain the storage limit: the maximum physical address that might be
+    used for storage throughout the lifetime of the VM.
+
+    The storage limit does not indicate currently usable storage, it may
+    include holes, standby storage and areas reserved for other means, such
+    as memory hotplug or virtio-mem devices. Other interfaces for detecting
+    actually usable storage, such as SCLP, must be used in conjunction with
+    this subfunction.
+
+    Note that the storage limit can be larger, but never smaller than the
+    maximum storage address indicated by SCLP via the "maximum storage
+    increment" and the "increment size".
+
 
 DIAGNOSE function code 'X'501 - KVM breakpoint
 ----------------------------------------------
-- 
2.46.1