Messages in this thread | | | Date | Thu, 20 Dec 2012 00:40:12 +0100 | From | Borislav Petkov <> | Subject | Re: [tip:x86/microcode] x86/microcode_intel_early.c: Early update ucode on Intel's CPU |
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On Wed, Dec 19, 2012 at 03:22:13PM -0800, H. Peter Anvin wrote:
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> 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.
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