Date: Sun, 5 Oct 2003 15:19:51 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Peter Wemm <peter@wemm.org> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/i386/i386 locore.s Message-ID: <20031005145547.X3175@gamplex.bde.org> In-Reply-To: <20031004065103.EBE312A7EA@canning.wemm.org> References: <20031004065103.EBE312A7EA@canning.wemm.org>
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On Fri, 3 Oct 2003, Peter Wemm wrote:
> Peter Wemm wrote:
>
> > 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.
>
> I'm not sure, now that I think about it more, I think Bruce may have tried
> to tell me about this once or twice before. Possibly when I was tinkering
> with pmap_mapdev last time.
I only remember complaining about the read-onlyness of the text section
being broken by 4MB pages. This still seems to be broken. It now seems
to be broken even in the !PSE case -- we now map r/w from btext to KERNend
where we used to map r/o from btext to etext and r/w from etext to KERNend.
My kernel was affected by the write-only page 0 in a different way. I
had quick-fixed the setting clean-reboot signature (0x1234 at 0x472
physical) by setting it in cpu_reset_real():
%%%
diff -c2 src/sys/i386/i386/vm_machdep.c~ src/sys/i386/i386/vm_machdep.c
*** src/sys/i386/i386/vm_machdep.c~ Sat Aug 30 19:35:06 2003
--- src/sys/i386/i386/vm_machdep.c Sat Aug 30 20:36:33 2003
***************
*** 531,534 ****
--- 509,522 ----
{
+ #ifndef PC98
+ /*
+ * Tell the BIOS to warm boot. XXX magic.
+ * XXX this depends on brokenness of readonlyness of the text
+ * section caused by 4MB pages.
+ */
+ if (cpu_feature & CPUID_PSE && rcr4() & CR4_PSE && panicstr == NULL)
+ *(short *)(KERNBASE + 0x472) = 0x1234;
+ #endif
+
#ifdef PC98
/*
%%%
The point of this signature has been defeated since 386BSD-0.0 by setting
it in locore.s. The above failed for obvious reasons when 4MB pages stopped
affecting page 0.
Bruce
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