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

[Igor Mammedov <imammedo@redhat.com>]

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.

> 
> 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;
>      }
>