Re: [Xen-devel] do_set_gdt

[Kip Macy <kmacy@xxxxxxxxxxx>]

> > You'll also want to make sure that you don't put other stuff in the last
> > page which hold the GDT table and align the GDT table to a page boundary:
> > lgdt allows the gdt to be anywhere while for Xen you have to put it at the
> > beginning of a page, can't really use the rest of the last page for much
> > else and have to keep the pages around.
>
> Yes, this is all correct. On first glance I thought this was a bug (I
> thought the code was deciding whether a particular GDT entry could be
> updated by the guest).
>


Yes, but you have to pass in at least a page which == 512 entries. So if
I'm only using the first 8 entries, there is no reason Xen can't use
256-296. Passing in LAST_RESERVED_ENTRY + 1, seems a little contrived
when it is only the first 8 that I care about. A better approach would
be to insist that entries 256-296 are set to 0 in the case where the
user sets nentries >= FIRST_RESERVED_ENTRY.


                        -Kip


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