Re: [Qemu-devel] [PATCH] pc-dimm: fix checking for backend memory size

[Zhu Guihua <zhugh.fnst@cn.fujitsu.com>]

On Mon, 2015-01-19 at 16:55 +0100, Igor Mammedov wrote:
> On Fri, 16 Jan 2015 13:45:06 +0800
> Zhu Guihua <zhugh.fnst@cn.fujitsu.com> wrote:
> 
> > If hot add 100MiB memory like this:
> > (monitor) object_add memory-backend-ram,id=ram0,size=100M
> > (monitor) device_add pc-dimm,id=d0,memdev=ram0
> > 
> > The hotplug operation will faile, and the guest will print error message:
> > Section-unaligned hotplug range: start 0x100000000, size 0x6400000
> > acpi PNP0C80:00: add_memory failed
> > acpi PNP0C80:00: acpi_memory_enable_device() error
> > 
> > Then I found that, according to the func check_hotplug_memory_range() in linux
> > kernel, backend memory size must be multiple of 128MiB, not 2MiB.
> It's linux limitation, Windows guests work just fine with small blocks.
> 
> It should be fixed in linux kernel or/and limitation should be enforced by
> libvirt/virt-install which knows what type of guest it installs/runs.
> 

Got it.
Thanks for your explanation.

Regards,
Zhu

> > 
> > So this patch checks whether backend memory size is multiple of 128MiB.
> > 
> > Signed-off-by: Zhu Guihua <zhugh.fnst@cn.fujitsu.com>
> > ---
> >  hw/mem/pc-dimm.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/hw/mem/pc-dimm.c b/hw/mem/pc-dimm.c
> > index d431834..3b8a015 100644
> > --- a/hw/mem/pc-dimm.c
> > +++ b/hw/mem/pc-dimm.c
> > @@ -161,9 +161,9 @@ uint64_t pc_dimm_get_free_addr(uint64_t address_space_start,
> >          goto out;
> >      }
> >  
> > -    if (QEMU_ALIGN_UP(size, align) != size) {
> > +    if (QEMU_ALIGN_UP(size, align * 64) != size) {
> >          error_setg(errp, "backend memory size must be multiple of 0x%"
> > -                   PRIx64, align);
> > +                   PRIx64, align * 64);
> >          goto out;
> >      }
> >  
>