Re: [Xen-devel] Re: x86_64 SMP support (status update)

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 27 Jun 2005, at 22:52, Chris Wright wrote:

> Yes, the table is in arch/xen/x86_64/kernel/head.S (cpu_gdt_table, 
> which
> has 16 8 byte entries per cpu).  However rather than using that table 
> directly,
> we must copy the entries into a per cpu page.  Xen side has assumptions
> regarding gdt being page sized (8 bytes * 512 entries, e.g. in
> xen/arch/x86/mm.c in alloc_segdesc_page).  That help?
Xen makes a shadow mapping of the per-vcpu gdt in its own address 
space. This, coupled with Xen reserving the last 2 pages of GDT entries 
for itself, requires every GDT to start on a page boundary. So, even 
though per-cpu gdts are not page-aligned they must be at least one page 
in size.
 -- Keir


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