[External] Re: [PATCH] qemu.conf: add max-ram-below-4g option

[Zhiyong Ye]

I agree with you. If it is added to the XML file, where should it be
placed? I think the following may be OK:
<domain>
  ...
  <maxMemory slots='16' unit='KiB'>1524288</maxMemory>
  <memory unit='KiB'>524288</memory>
  <currentMemory unit='KiB'>524288</currentMemory>
  <below4gMemory unit='GiB'>2</below4gMemory>
  ...
</domain>

Peter Krempa <pkrempa at redhat.com> 于2021年4月21日周三 下午4:46写道：

> On Wed, Apr 21, 2021 at 16:25:28 +0800, yezhiyong wrote:
> > Limit the amount of ram below 4G. This helps in scenarios like
> > GPU passthrough when the GPA used by DMA device is conflict with
> > the decode window of a host bridge and the address translation
> > request to iommu isn't launched, which causes address overlapping.
> > Note that currently this can be triggered by some abnormal behavior
> > of hardware.
> >
> > In the general case, this option needs to be configured when virtual
> > machines share the same host, which is why using qemu.conf to support
> > per-host configuration.
>
> Is this really something you want to set for EVERY VM all the time,
> because it doesn't seem to me to be the case.
>
> If there is any reason not to have this for all VMs it must not be done
> via qemu.conf option but rather a XML knob.
>
> > Signed-off-by: yezhiyong <yezhiyong at bytedance.com>
> > Signed-off-by: zhenwei pi <pizhenwei at bytedance.com>
> > Signed-off-by: zhangruien <zhangruien at bytedance.com>
> > ---
> >  src/qemu/qemu.conf      | 8 ++++++++
> >  src/qemu/qemu_command.c | 4 ++++
> >  src/qemu/qemu_conf.c    | 5 +++++
> >  src/qemu/qemu_conf.h    | 1 +
> >  4 files changed, 18 insertions(+)
> >
> > diff --git a/src/qemu/qemu.conf b/src/qemu/qemu.conf
> > index 8722dc169c..f09c89486e 100644
> > --- a/src/qemu/qemu.conf
> > +++ b/src/qemu/qemu.conf
> > @@ -898,6 +898,14 @@
> >  # NOTE: big files will be stored here
> >  #memory_backing_dir = "/var/lib/libvirt/qemu/ram"
> >
> > +# Limit the amount of ram below 4G. This helps in scenarios like
> > +# GPU passthrough when the GPA used by DMA device is comflict with
> > +# the decode window of a host bridge and the address translation
> > +# request to iommu isn't launched, which causes address overlapping.
> > +# Note that currently this can be triggered by some abnormal behavior
> > +# of hardware.
> > +#max_ram_below_4g = "2G"
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://listman.redhat.com/archives/libvir-list/attachments/20210421/eddde37c/attachment-0001.htm>