linux-kernel - Re: [PATCH v2 5/7] virtio-mem: s390 support

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Message-ID: <20241015083750.7641-D-hca@linux.ibm.com>
Date: Tue, 15 Oct 2024 10:37:50 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
        linux-doc@...r.kernel.org, kvm@...r.kernel.org,
        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>, Mario Casquero <mcasquer@...hat.com>
Subject: Re: [PATCH v2 5/7] virtio-mem: s390 support

On Mon, Oct 14, 2024 at 09:16:45PM +0200, David Hildenbrand wrote:
> On 14.10.24 20:48, Heiko Carstens wrote:
> > On Mon, Oct 14, 2024 at 04:46:17PM +0200, David Hildenbrand wrote:
> > > to dump. Based on this, support for dumping virtio-mem memory can be
> > Hm.. who will add this support? This looks like a showstopper to me.
> 
> The cover letter is clearer on that: "One remaining work item is kdump
> support for virtio-mem memory. This will be sent out separately once initial
> support landed."
> 
> I had a prototype, but need to spend some time to clean it up -- or find
> someone to hand it over to clean it up.
> 
> I have to chose wisely what I work on nowadays, and cannot spend that time
> if the basic support won't get ACKed.
> 
> > Who is supposed to debug crash dumps where memory parts are missing?
> 
> For many production use cases it certainly needs to exist.
> 
> But note that virtio-mem can be used with ZONE_MOVABLE, in which case mostly
> only user data (e.g., pagecache,anon) ends up on hotplugged memory, that
> would get excluded from makedumpfile in the default configs either way.
> 
> It's not uncommon to let kdump support be added later (e.g., AMD SNP
> variants).

I'll leave it up to kvm folks to decide if we need kdump support from
the beginning or if we are good with the current implementation.