Re: [Xen-devel] [PATCH] add pae flag to xen/Rules.mk

[Karen White <kawhite@xxxxxxxxxx>]

On Tue, 2005-03-29 at 08:49 +0100, Keir Fraser wrote:
> On 29 Mar 2005, at 01:26, Karen White wrote:
> 
> > Add pae flag to xen/Rules.mk.   Adds -DCONFIG_PAE to CFLAGS if pae is
> > set and target is x86_32
> >
> > Signed-off-by: Karen White <kawhite@xxxxxxxxxx>
> 
> We'll add a CONFIG_PAE if it's needed, when the PAE support gets 
> checked in. We are actually hoping to have a 'dual boot' Xen that will 
> select PAE (or not) depending on the memory size and optional boot-time 
> parameter.
Keir,

So the boot-time parameter will be used to conditionally choose if you
need level-2 or level-3 page tables, etc?  Last week Ian responded to my
comments about the #define, and previous emails with Gerd have described
the PAE support will be compiled in.

Do you, Gerd, and Ian have a current high-level design?   Below are my
comments and Ian's responses about the #define and Gerd sent email today
about also using an #ifdef to determine which page table header file to
include.

Karen


Ian's responses to my config questions:
> To be able to add the PAE specific changes, we need to settle on a
> #define for ifdefing around them in the core Xen code.
> 
> What about CONFIG_PAE?  We could add this to asm-x86/config.h if pae=y
> is passed in on the make line (via Rules.mk)

CONFIG_PAE seems reasonable.
 
> New parallel files vs. ifdef existing files:
> 
> Has anyone settled on if the PAE code is going into the files under
> xen/arch/x86/x86_32, using #ifdef's for PAE, or are you 
> planning to add
> a parallel directory to x86_32 and x86_64 under xen/arch?

Most of the changes can be hidden in header files. There should be no
need for extra c files.

> Same question for headers.  Are you adding the 3-level page tables to
> the existing include/asm-x86/x86_32/page.h using #ifdef's or adding a
> new directory parallel to x86_32 and x86_64 which would have a new
> page.h, etc?

Having a separate 2 and 3 level file that is conditionally included by
x86_32/page.h would seem to be the best approach.> Same question for
headers.  Are you adding the 3-level page tables to
> the existing include/asm-x86/x86_32/page.h using #ifdef's or adding a
> new directory parallel to x86_32 and x86_64 which would have a new
> page.h, etc?

I'd create include/asm-x86/x86_32/page-2l.h and page-3l.h and let
page.h include the correct one depending on CONFIG_X86_PAE (and also
have the common stuff there).

Ian





> 
>   -- Keir
> 
> 
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