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SubjectRe: [PATCH, experimental] i386 Allow the fixmap to be relocated at boot time
* Zachary Amsden (zach@vmware.com) wrote:
> Your patch looks good, although the minimal change to subarch is to
> merely have __FIXADDR_TOP defined by the sub-architecture. Is there any
> additional benefit to moving the fixmaps into the subarch - i.e. moving
> subarch-specific pieces out of mach-default?

As you've identified, so subarch can put whatever wonky junk
it needs in there.

> I guess there is. For example include/asm-i386/mach-visws/mach_fixmap.h
> could do this:
>
> #define SUBARCH_FIXMAPS \
> FIX_CO_CPU, /* Cobalt timer */ \
> FIX_CO_APIC, /* Cobalt APIC Redirection Table */ \
> FIX_LI_PCIA, /* Lithium PCI Bridge A */ \
> FIX_LI_PCIB, /* Lithium PCI Bridge B */
>
> Then include/asm-i386/fixmap.h includes <mach_fixmap.h>, for which the
> default is an empty define for SUBARCH_FIXMAPS.

nice.

> Also, it seems reasonable that people may want to poke holes in high
> linear space for other hypervisor projects, research, or performance
> reasons without having to build a custom sub-architecture just for
> that. So I think there is some benefit to making the hole size a
> general configurable option (with defaults depending on the sub-arch you
> select).

It needs to have tangible value for in-tree code. Seems worthwhile to
play with it a bit though.

thanks,
-chris
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