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: Mon, 13 Jul 2020 11:12:43 +0200 [thread overview]
Message-ID: <20200713091243.GB4359@osiris> (raw)
In-Reply-To: <10bdd986-c474-278d-ed6a-193d9a45fe33@redhat.com>
On Fri, Jul 10, 2020 at 05:24:07PM +0200, David Hildenbrand wrote:
> 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.
Ok, now I see the context. Christian added my just to cc on this
specific patch.
So if I understand you correctly, then you want to use diag 260 in
order to figure out how much memory is _potentially_ available for a
guest?
This does not fit to the current semantics, since diag 260 returns the
address of the highest *currently* accessible address. That is: it
does explicitly *not* include standby memory or anything else that
might potentially be there.
So you would need a different interface to tell the guest about your
new hotplug memory interface. If sclp does not work, then maybe a new
diagnose(?).
next prev parent reply other threads:[~2020-07-13 9:13 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-08 18:51 [PATCH RFC 0/5] s390x: initial support for virtio-mem David Hildenbrand
2020-07-08 18:51 ` [PATCH RFC 1/5] s390x: move setting of maximum ram size to machine init David Hildenbrand
2020-07-08 18:51 ` [PATCH RFC 2/5] s390x: implement diag260 David Hildenbrand
2020-07-09 10:37 ` Cornelia Huck
2020-07-09 17:54 ` David Hildenbrand
2020-07-10 8:32 ` David Hildenbrand
2020-07-10 8:41 ` David Hildenbrand
2020-07-10 9:19 ` Cornelia Huck
2020-07-13 11:54 ` Christian Borntraeger
2020-07-13 12:11 ` Cornelia Huck
2020-07-13 12:13 ` Christian Borntraeger
2020-07-09 10:52 ` Christian Borntraeger
2020-07-09 18:15 ` David Hildenbrand
2020-07-10 9:17 ` David Hildenbrand
2020-07-10 12:12 ` David Hildenbrand
2020-07-10 15:18 ` Heiko Carstens
2020-07-10 15:24 ` David Hildenbrand
2020-07-10 15:43 ` Heiko Carstens
2020-07-10 15:45 ` David Hildenbrand
2020-07-13 9:12 ` Heiko Carstens [this message]
2020-07-13 10:27 ` David Hildenbrand
2020-07-13 11:08 ` Christian Borntraeger
2020-07-15 9:42 ` David Hildenbrand
2020-07-15 10:43 ` Heiko Carstens
2020-07-15 11:21 ` David Hildenbrand
2020-07-15 11:34 ` Heiko Carstens
2020-07-15 11:42 ` David Hildenbrand
2020-07-15 16:14 ` Heiko Carstens
2020-07-15 17:38 ` David Hildenbrand
2020-07-15 17:51 ` David Hildenbrand
2020-07-20 14:43 ` Heiko Carstens
2020-07-20 15:43 ` David Hildenbrand
2020-07-08 18:51 ` [PATCH RFC 3/5] s390x: prepare device memory address space David Hildenbrand
2020-07-09 10:59 ` Cornelia Huck
2020-07-10 7:46 ` David Hildenbrand
2020-07-08 18:51 ` [PATCH RFC 4/5] s390x: implement virtio-mem-ccw David Hildenbrand
2020-07-09 9:24 ` Cornelia Huck
2020-07-09 9:26 ` David Hildenbrand
2020-07-08 18:51 ` [PATCH RFC 5/5] s390x: initial support for virtio-mem David Hildenbrand
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