Eric W. Biederman wrote:
> Ok. Although we can hoist the bss zeroing, if everything needs it.
>
It will if we're booting out of bzImage; the bss won't be clear in that
case.
> Hmm. I'm wondering about the segment reload and how much of a problem
> that is. My memory says that segment reloads are not actually a
> privileged operation, so we may be able to support this even in
> paravirt mode. How hard would that be to support? The segment
> we reload is a fixed part of our boot protocol.
>
The problem is not the reloads themselves, but what you're reloading
them with. If we come up under Xen, then it will provide a default GDT
and pre-load the segments with flat 4G(-ish) selectors - but the
selectors won't be the normal Linux ones.
So if we reload using a constant selector, then that will break under
Xen. But if we do a:
mov %cs, %eax
mov %eax, %ds
// etc
sequence then it should be fine. This will work even for loading %ss,
since the %cs CPL will equal the RPL needed for %ss.
J
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