On Wed, Dec 19, 2012 at 03:22:13PM -0800, H. Peter Anvin wrote:
[ … ]
> Now, calming down a little bit, we are definitely dealing with BIOS
> engineers and so f*ckups are going to happen, again and again.
Yeppers.
> The only truly "safe" option is to limit early mappings to 4K pages.
> This is highly undesirable for a bunch of reasons. Reducing mapping
> granularity to 2M rather than 1G (what Yinghai is proposing) does reduce
> the exposure somewhat; it would be interesting to gather trap statistics
> and try to get a feel for if this actually changes the boot time
> measurably or not.
This is done on the BSP, right? So we can measure it how long it takes
by taking TSC values of start and end.
> The other bit is that building the real kernel page tables iteratively
> (ignoring the early page tables here) is safer, since the real page
> table builder is fully aware of the memory map. This means any
> "spillover" from the early page tables gets minimized to regions where
> there are data objects that have to be accessed early.
That shouldn't be a "lot", relatively speaking.
> Since Yinghai already had iterative page table building working, I
> don't see any reason to not use that capability.
>
> Thoughts?
Sounds doable but we should take a hard look at the patches so that we
don't miss anything.
Also, I don't know how stuff like that would be approached for a wider
testing - I mean, it is a serious change in x86 boot code and there will
be issues.
Hmm.
--
Regards/Gruss,
Boris.
Sent from a fat crate under my desk. Formatting is fine.
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