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From: Peter Wemm <peter@FreeBSD.org>
Date: Fri, 3 Oct 2003 23:30:56 -0700 (PDT)
To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org,
	cvs-all@FreeBSD.org
X-FreeBSD-CVS-Branch: HEAD
Subject: cvs commit: src/sys/i386/i386 locore.s
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peter       2003/10/03 23:30:56 PDT

  FreeBSD src repository

  Modified files:
    sys/i386/i386        locore.s 
  Log:
  Emulate bugs in the old PSE code so that apm works again.
  
  I do not yet understand why, but apm *depended* on the fact that the old
  PSE code caused the first 1MB of ram to be mapped read/write because it
  was in the same 4MB page as the kernel text+data+bss blob.
  
  If anybody ever tried DISABLE_PSE before, apm would not work.
  
  If your cpu did not have PSE, apm would not work there either (eg: 486).
  
  This bug has been around for a Very Long Time.
  
  The Pentium-4-fix commits did not emulate this unintended side effect of
  the PSE post-early-boot fixup, and thus apm blew up.  I've added a hack to
  emulate the bug until either apm is fixed or we set fire to our bridges.
  
  This is bad though because it gives kernel mode code the opportunity
  to accidently write to the first few megs of the general page pool
  which is remapped at KERNBASE.  It needs to be fixed properly.
  
  Revision  Changes    Path
  1.177     +5 -0      src/sys/i386/i386/locore.s