Re: [Xen-devel] do_set_gdt

[Christian Limpach <chris@xxxxxx>]

> 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.

I'd find it disturbing if we passed in 8 and Xen would then change entries
9-LAST_RESERVED_ENTRY[*].  Right now Xen only changes entries within the
memory you offered it for storing the GDT, so you are implicitly aware that
memory for at least LAST_RESERVED_ENTRY entries will be used for the GDT
table...

[*] Xen would have to zero/invalidate entries 9-FIRST_RESERVED_ENTRY

> 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.

What would that accomplish?  Besides that it wouldn't work:  we copy Xen's
entries into the table which would make the table fail the 0-check the next
time you call set_gdt...

    christian



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