Re: [PATCH] xen: convert p2m to a 3 level tree - partial revert

[Stefan Bader <stefan.bader@canonical.com>]

On 01/27/2011 03:48 PM, Daniel Kiper wrote:
> Hi,
> 
> Durning work on Xen memory hotplug I discoverd that
> 2.6.38-rc2 does not boot on domU. After some investigation
> it appeared that 58e05027b530ff081ecea68e38de8d59db8f87e0
> commit changed CONFIG_XEN_MAX_DOMAIN_MEMORY constant value
> to 128. This change does not allow to boot kernel on domU
> with small memory size (I could confirm that it is even
> not possible to boot kernel on domU with 2 GiB). Guest
> crash silently without any warning. Durning further
> research I found out that there is another commit published
> recently (8e1b4cf2108488ccfb9a3e7ed7cd85a435e01d4b) which attempts
> to fix this issue, however, it does not work on my platform.
> I decided to reenable CONFIG_XEN_MAX_DOMAIN_MEMORY option in
> kernel config and enable users to choose resonable values for
> their machines until better fix will be published. I think this
> solution is good because allow users to boot domU with newest
> kernel and allow developers to continue their work without
> time presure which could lead to new bugs.
> 

Have you tried with a version that contains

commit 8e1b4cf2108488ccfb9a3e7ed7cd85a435e01d4b
Author: Stefan Bader <stefan.bader@canonical.com>
Date:   Thu Jan 20 15:38:23 2011 +0100

    xen: p2m: correctly initialize partial p2m leaf

I still may need to send a follow up to add a matching RESERVE_BRK, but at least
I was able to boot small DomU's again.

-Stefan
> This patch applies cleanly to current Linus' kernel tree.
> 
> Signed-off-by: Daniel Kiper <dkiper@net-space.pl>
> ---
>  arch/x86/xen/Kconfig |   11 +++++++----
>  1 files changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
> index 5b54892..a234b9a 100644
> --- a/arch/x86/xen/Kconfig
> +++ b/arch/x86/xen/Kconfig
> @@ -29,12 +29,15 @@ config XEN_PVHVM
>  	depends on X86_LOCAL_APIC
>  
>  config XEN_MAX_DOMAIN_MEMORY
> -       int
> -       default 128
> +       int "Maximum allowed size of a domain in gigabytes"
> +       default 8 if X86_32
> +       default 32 if X86_64
>         depends on XEN
>         help
> -         This only affects the sizing of some bss arrays, the unused
> -         portions of which are freed.
> +         The pseudo-physical to machine address array is sized
> +         according to the maximum possible memory size of a Xen
> +         domain.  This array uses 1 page per gigabyte, so there's no
> +         need to be too stingy here.
>  
>  config XEN_SAVE_RESTORE
>         bool