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

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

> Er. We don't really but I think this if needs to be:
> 
>     /*
>      * Page align regions.
>      *
>      * Reduce RAM regions and expand other (reserved) regions.
>      */
>     if (type == E820_RAM || type == E820_UNUSABLE) {
>       start = PAGE_ALIGN(start);
>         end  &= ~((u64)PAGE_SIZE - 1);
>     } else {
>         start &= ~((u64)PAGE_SIZE - 1);
>         end = PAGE_ALIGN(start);
>     }
> 
> So reserved regions also become page aligned (which is part of the fix
> for the dmidecode bug).

I am not sure actually that is required for the e820_* calls. As those
are used by 'ioremap' and memory buddy system and they only care about
the RAM regions. Everybody else assumes that the "gaps" and "anything-but
-RAM-regions" are OK - as long as they don't touch the RAM regions.

It certainly is required for the set_phys_to_identity(..) call.

I am trying here to be sure we don't mess it up - and I don't know
what the right answer is for e820_* calls. Well, I do know what the
right answer if for RAM regions - they must be page-aligned. But
for reserved/non-RAM/ACPI/ACPI-NVS... ?

BIOS-e820: 00000000dfe8ac00 - 00000000dfe8cc00 (ACPI NVS)
BIOS-e820: 00000000dfe8cc00 - 00000000dfe8ec00 (ACPI data)
.. snip..
reserve RAM buffer: 00000000dfe8ac00 - 00000000dfffffff

or say:
BIOS-e820: 00000000bff66f00 - 00000000bff76300 (ACPI data)
..
[    1.026860] reserve RAM buffer: 00000000bff66f00 - 00000000bfffffff

They all seem to work OK without being page-aligned.

I think we can drop the page-alignment on non-RAM regions when we
give it to e820_*. We want to diverge as little as possible from what baremetal
does.

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