Re: [Xen-devel] Re: xen: memory initialization/balloon fixes (#3)

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

> > (XEN) Xen-e820 RAM map:
> > (XEN)  0000000000000000 - 000000000009d800 (usable)
> 
> It's because it's not correctly handling the half-page of RAM at the end
> of this region.
> 
> I don't have access to any test boxes with a dodgy BIOS like this so can
> you test this patch?  If it works I'll fold it in and post an updated
> series.

It works. Albeit I think we are going to hit a problem with dmidecode
if the DMI data is right in the reserved region

(http://lists.xensource.com/archives/html/xen-devel/2011-09/msg01299.html)

As in, if it starts in 9D800 - we consider 0->9d as RAM PFN, and 9e->100 as 1-1
mapping.

I am thinking that perhaps the call to xen_set_phys_identity, where
we call PFN_UP(x) should be replaced with PFN_DOWN(x). That way
we would consider 0>9c as RAM PFN and 9D->100 as 1-1 mapping.

That would imply a new patch to your series naturally.
> 
> Can you remember why this page alignment was required?  I'd like to

The e820_* calls define how the memory subsystem will use it.
It ended at some point assuming that the full page is RAM even thought
it was only half-RAM and tried to use it and blew the machine up.

The fix was to make the calls to the e820_* with size and regions
that were page-aligned.

Anyhow, here is what the bootup looks now:

[    0.000000] Freeing  9e-a0 pfn range: 2 pages freed
[    0.000000] 1-1 mapping on 9e->a0
[    0.000000] Freeing  a0-100 pfn range: 96 pages freed
[    0.000000] 1-1 mapping on a0->100
[    0.000000] Freeing  7fff0-80000 pfn range: 16 pages freed
[    0.000000] 1-1 mapping on 7fff0->80000
[    0.000000] Freeing  cfef0-cfef5 pfn range: 5 pages freed
[    0.000000] 1-1 mapping on cfef0->cfef5
[    0.000000] Freeing  cfef5-cff7f pfn range: 138 pages freed
[    0.000000] 1-1 mapping on cfef5->cff7f
[    0.000000] Freeing  cff7f-d0000 pfn range: 129 pages freed
[    0.000000] 1-1 mapping on cff7f->d0000
[    0.000000] Freeing  d0000-f0000 pfn range: 131072 pages freed
[    0.000000] 1-1 mapping on d0000->f0000
[    0.000000] Freeing  f0000-f4b58 pfn range: 19288 pages freed
[    0.000000] 1-1 mapping on f0000->fec10
[    0.000000] 1-1 mapping on fec10->fee01
[    0.000000] 1-1 mapping on fee01->100000
[    0.000000] Released 150746 pages of unused memory
[    0.000000] Set 196994 page(s) to 1-1 mapping
[    0.000000] BIOS-provided physical RAM map:
[    0.000000]  Xen: 0000000000000000 - 000000000009d000 (usable)
[    0.000000]  Xen: 000000000009d800 - 0000000000100000 (reserved)
[    0.000000]  Xen: 0000000000100000 - 000000007fff0000 (usable)
[    0.000000]  Xen: 000000007fff0000 - 0000000080000000 (reserved)


> update the comment with the reason because the bare-metal x86 memory
> init code doesn't appear to fixup the memory map in this way.
> 
> diff --git a/arch/x86/xen/setup.c b/arch/x86/xen/setup.c
> index 986661b..e473c4c 100644
> --- a/arch/x86/xen/setup.c
> +++ b/arch/x86/xen/setup.c
> @@ -178,6 +178,19 @@ static unsigned long __init xen_get_max_pages(void)
>       return min(max_pages, MAX_DOMAIN_PAGES);
>  }
> 
> +static void xen_e820_add_region(u64 start, u64 size, int type)
> +{
> +     u64 end = start + size;
> +
> +     /* Align RAM regions to page boundaries. */
> +     if (type == E820_RAM || type == E820_UNUSABLE) {

Hm, do we care about E820_UNUSABLE to be page aligned?
If so, please comment why.

> +             start = PAGE_ALIGN(start);

Is that actually safe? Say it starts a 9ffff? We would
end up using 9f000 which is not right.

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