Xen devel - Feb 2006 - difference between PGT_gdt_page and PGT_ldt_page

Is there any particular reason why there cannot just be a PGT_descr_page,
combining the two currently existing types?
Even if it''s only a page, I''d want to avoid wasting memory for
nothing, and i386''s default_ldt could easily move into
the same page cpu_gdt_table lives in. Alternatively one could also use
empty_zero_page here. Or do it like on x86-64,
where the symbol doesn''t exist at all, and knowledge about it being all
zeroes is used where needed. Jan

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On 15 Feb 2006, at 09:09, Jan Beulich wrote:
> Is there any particular reason why there cannot just be a 
> PGT_descr_page, combining the two currently existing types?
> Even if it''s only a page, I''d want to avoid wasting
memory for
> nothing, and i386''s default_ldt could easily move into
> the same page cpu_gdt_table lives in. Alternatively one could also use 
> empty_zero_page here. Or do it like on x86-64,
> where the symbol doesn''t exist at all, and knowledge about it
being
> all zeroes is used where needed. Jan
If default_ldt can be replaced by empty_zero_page, why do we need a 
default LDT at all?

The page types could quite easily be merged. The main problem is that 
all descriptor tables need to be page aligned. We could get rid of that 
restriction for LDTs I think.

  -- Keir


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>If default_ldt can be replaced by empty_zero_page, why do we need a 
>default LDT at all?
That would be one of the implied questions. I assume this is done to minimize
the delta to native code, which
needlessly has this, too.

Jan

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>The page types could quite easily be merged. The main problem is that 
>all descriptor tables need to be page aligned. We could get rid of that 
>restriction for LDTs I think.
Wouldn''t that imply that you don''t need a special PGT_ldt_page
type then anymore?

Jan

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