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Date: Tue, 3 Nov 2015 12:25:20 +0100
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH 1/2] dataplane: simplify
 indirect descriptor read
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To: Stefan Hajnoczi <stefanha@gmail.com>
Cc: qemu-block@nongnu.org, qemu-devel@nongnu.org, Stefan Hajnoczi <stefanha@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

On Mon, 2 Nov 2015 17:43:16 +0000
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Wed, Oct 28, 2015 at 05:48:02PM +0200, Michael S. Tsirkin wrote:
> > Use address_space_read to make sure we handle the case of an indirect
> > descriptor crossing DIMM boundary correctly.
> > 
> > Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
> > ---
> > 
> > Warning: compile-tested only.
> 
> Test (with your follow-up patch squashed in) with 6 4KB seqeuential read
> processes on running successfully.
> 
> I didn't test the DIMM boundary case.  Igor: what is the easiest way to
> reproduce the DIMM boundary crossing?

I've tested it, here is QEMU CLI:
qemu-system-x86_64 -enable-kvm -enable-kvm  -m 128M,slots=250,maxmem=32G  -drive if=none,id=hd,file=rhel72,cache=none,aio=native,format=raw -device virtio-blk,drive=hd,scsi=off,config-wce=off,x-data-plane=on `for i in $(seq 0 15); do echo -n "-object memory-backend-ram,id=m$i,size=10M -device pc-dimm,id=dimm$i,memdev=m$i "; done`

boot and then do:
dd if=/dev/vda of=/dev/null bs=16M

without fix it hangs either at boot time or when doing 'dd'