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From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <e2e0ff2b-139e-0582-c8f9-9a716780ff1f@redhat.com>
Date: Thu, 7 Jun 2018 13:02:51 +0200
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Subject: Re: [Qemu-devel] An emulation failure occurs,
 if I hotplug vcpus immediately after the VM start
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To: David Hildenbrand <david@redhat.com>, "Gonglei (Arei)" <arei.gonglei@huawei.com>, Igor Mammedov <imammedo@redhat.com>, xuyandong <xuyandong2@huawei.com>
Cc: Zhanghailiang <zhang.zhanghailiang@huawei.com>, "wangxin (U)" <wangxinxin.wang@huawei.com>, lidonglin <lidonglin@huawei.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, "Huangweidong (C)" <weidong.huang@huawei.com>

On 07/06/2018 12:37, David Hildenbrand wrote:
>=20
> I have a related requirement, which would be to atomically grow a
> memory regions. So instead of region_del(old)+region_add(new), I would
> have to do it in one shot (atomically).
>=20
> AFAICS an atomic replace of the memory map would work for this, too.
> However I am not sure how we want to handle all kinds of tracking data
> that is connected to e.g. x86 memory slots (e.g. rmap, dirty bitmap ...=
).

The dirty bitmap would be synced in kvm_region_del (so it's not true
that kvm_region_del would disappear, but almost :)).

The rmap is more interesting.  Perhaps it can be just rebuilt on every
KVM_SET_USER_MEMORY_REGIONS call.

Paolo