Re: [PATCH] x86/microcode_intel_early.c: Get 32-bit physical addressby __pa_nodebug()

From: Yinghai Lu
Date: Tue Mar 19 2013 - 19:15:17 EST

On Tue, Mar 19, 2013 at 8:04 AM, Fenghua Yu <fenghua.yu@xxxxxxxxx> wrote:
> From: Fenghua Yu <fenghua.yu@xxxxxxxxx>
> In 32-bit, __pa_symbol() in CONFIG_DEBUG_VIRTUAL accesses kernel data (e.g.
> max_low_pfn) that haven't been setup yet in such early boot phase. To fix the
> issue, __pa_nodebug() replaces __pa_symbol() to get a global symbol's physical
> address.

That explanation is not precise.

__phys_addr in 32bit when DEBUG_VIRTUAL is set, it does have check
/* max_low_pfn is set early, but not _that_ early */
if (max_low_pfn) {
the reason should be:
in head_32.S, 32bit flat mode, you need to switch to phys addr to access
global variable max_low_pfn.


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