Re: [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit v2

Alexander van Heukelum
2008-03-04T16:51:28Z

On Tue, 04 Mar 2008 07:18:48 -0800, "Jeremy Fitzhardinge"
<jeremy@goop.org> said:
> Mark McLoughlin wrote:
> > This is a bit magic, is it worth splitting it out as something like
> > is_paravirt_environment() ?
> >
>
> Yes, is_paravirt() already exists for this purpose.

Hi,

If it exists, it is well-hidden. A grep for is_paravirt on the testing
tree turns up nothing. Did you get the name right?

> The code looking at the boot params will only work if we actually booted
> via the paravirt Linux boot protocol, which Xen doesn't at present.

I chose to code it exactly this way, because it is what is used in
head_32.S to choose how to start the kernel. Or is this code not
executed at all?

[excerpt form head_32.S]
cmpw $0x207, pa(boot_params + BP_version)
jb default_entry

/* Paravirt-compatible boot parameters. Look to see what
architecture
we're booting under. */
movl pa(boot_params + BP_hardware_subarch), %eax
cmpl $num_subarch_entries, %eax
jae bad_subarch

movl pa(subarch_entries)(,%eax,4), %eax
subl $__PAGE_OFFSET, %eax
jmp *%eax
[and]
subarch_entries:
.long default_entry /* normal x86/PC */
.long lguest_entry /* lguest hypervisor */
.long xen_entry /* Xen hypervisor */
num_subarch_entries = (. - subarch_entries) / 4
[end]

If this is indeed not executed, is there a way to detect whether
we can expect the environment to behave like a normal pc in terms
of magic addresses, bios areas, isa reserved address space and so
on?

Greetings,
Alexander
--
Alexander van Heukelum
heukelum@fastmail.fm

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