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Date: Wed, 24 Jul 2013 12:58:36 +0200
From: Vasilis Liaskovitis <vasilis.liaskovitis@profitbricks.com>
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Subject: Re: [Qemu-devel] [PATCH 00/16 RFC v6] ACPI memory hotplug
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To: Igor Mammedov <imammedo@redhat.com>
Cc: Hu Tao <hutao@cn.fujitsu.com>, qemu-devel@nongnu.org, pbonzini@redhat.com

On Wed, Jul 24, 2013 at 12:02:46PM +0200, Igor Mammedov wrote:
> On Wed, 24 Jul 2013 17:52:50 +0800
> Hu Tao <hutao@cn.fujitsu.com> wrote:
> 
> > v6 doesn't work here, things are going fine until online hotplugged
> > memory in guest.
> > 
> > steps:
> > 
> > 1. qemu cmd:
> > 
> >   ./x86_64-softmmu/qemu-system-x86_64 -enable-kvm -m 512,maxmem=2G,slots=1 \
> >   -hda /mnt/data/libvirt-images/hut-rhel6.3.img -L ../pc-bios-memhp/
> > 
> >   (bios is from MST's acpi tree)
> > 
> > 2. hot-plug a dimm:
> > 
> >   device_adddimm,id=d0,size=1G
> > 
> > 3. online hotplugged memory(in guest):
> > 
> >   echo 'onlone' > /sys/devices/system/memory/memory/32/state
> > 
> > then after several seconds the console prints error messages like:
> > 
> >   nommu_map_sg: overflow 107c15000+4096 of device mask ffffffff
> >   ata1.00: exception Emask 0x0 SAct 0x0 SErr 0x0 action 0x0
> >   ata1.00: cmd ca/00:10:d0:0d:a4/00:00:00:00:00/e0 tag 0 dma 8192 out
> >            res 50/00:00:08:09:e0/00:00:00:00:00/e0 Emask 0x40 (internal error)
> >   ata1.00: configured for MWDMA2
> >   ata1: EH complete
> > 
> >   (repeat)
> > 
> > and can't do any disk I/O.
> Looks like a guest bug where it tries to use high memory but assumes low one.

yes. Iirc booting the guest kernel with "swiotlb=force" option could also
work around this.

> if you boot guest with initial memory 4Gb then it wont hit issue or use FC18
> which doesn't have this problem.

thanks,

- Vasilis