Date: Sun, 5 Oct 2003 16:27:46 +1000 (EST) From: Bruce Evans <bde@zeta.org.au> To: Peter Wemm <peter@freebsd.org> Cc: cvs-all@freebsd.org Subject: Re: cvs commit: src/sys/i386/i386 locore.s machdep.c Message-ID: <20031005152153.T3175@gamplex.bde.org> In-Reply-To: <200310042204.h94M4sCW037135@repoman.freebsd.org> References: <200310042204.h94M4sCW037135@repoman.freebsd.org>
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On Sat, 4 Oct 2003, Peter Wemm wrote:
> peter 2003/10/04 15:04:54 PDT
>
> FreeBSD src repository
>
> Modified files:
> sys/i386/i386 locore.s machdep.c
> Log:
> Fix the apm problem for real. We leave the first 4K page for the bios to
> work in, but we had it mapped read-only. While this has always been the
> case, the PG_PS enable hack hid it and the apm bios code ended up taking
> advantage of it.
>
> Revision Changes Path
> 1.178 +0 -5 src/sys/i386/i386/locore.s
> 1.574 +6 -0 src/sys/i386/i386/machdep.c
This seems to be missing code for hasbrokenint12 case. Untested fix
(with related and unrelated style changes):
%%%
Index: machdep.c
===================================================================
RCS file: /home/ncvs/src/sys/i386/i386/machdep.c,v
retrieving revision 1.574
diff -u -2 -r1.574 machdep.c
--- machdep.c 4 Oct 2003 22:04:54 -0000 1.574
+++ machdep.c 5 Oct 2003 05:54:53 -0000
@@ -1505,7 +1530,14 @@
struct bios_smap *smap;
+ /*
+ * Change the mapping of the page at address zero from r/o to r/w
+ * so that vm86 can scribble on this page. Note that this page is
+ * not in the general free page pool.
+ */
+ pmap_kenter(KERNBASE, 0);
+
hasbrokenint12 = 0;
TUNABLE_INT_FETCH("hw.hasbrokenint12", &hasbrokenint12);
- bzero(&vmf, sizeof(struct vm86frame));
+ bzero(&vmf, sizeof(vmf));
bzero(physmap, sizeof(physmap));
basemem = 0;
@@ -1556,12 +1587,8 @@
/*
- * Map the page at address zero for the bios code to use.
- * Note that page zero is not in the general page pool.
- */
- pmap_kenter(KERNBASE, 0);
-
- /*
- * if basemem != 640, map pages r/w into vm86 page table so
- * that the bios can scribble on it.
+ * Map pages between basemem and ISA_HOLE_START, if any, r/w into
+ * the vm86 page table so that vm86 can scribble on them using
+ * the vm86 map too. XXX: why 2 ways for this and only 1 way for
+ * page 0, at least as initialized here?
*/
pte = (pt_entry_t *)vm86paddr;
@@ -1646,18 +1674,25 @@
}
- if (basemem == 0) {
- basemem = 640;
- }
+ /*
+ * XXX this function is horribly organized and has to the same
+ * things that it does above here.
+ */
+ if (basemem == 0)
+ basemem = 640;
if (basemem > 640) {
- printf("Preposterous BIOS basemem of %uK, truncating to 640K\n",
- basemem);
+ printf(
+ "Preposterous BIOS basemem of %uK; truncating to 640K\n",
+ basemem);
basemem = 640;
}
+ /*
+ * Let vm86 scribble on pages between basemem and
+ * ISA_HOLE_START, as above.
+ */
for (pa = trunc_page(basemem * 1024);
pa < ISA_HOLE_START; pa += PAGE_SIZE)
pmap_kenter(KERNBASE + pa, pa);
-
pte = (pt_entry_t *)vm86paddr;
for (i = basemem / 4; i < 160; i++)
%%%
This mainly moves the r/w mapping for page 0 earlier and rewrites
related comments (but not the big one about the first part of remapping
biosbasemem through ISA_HOLE_START that most needs rewriting). The
mapping of page 0 has nothing to do with basemem unless basemem == 0
in which case we probably crashed already.
Unfinished related details:
- Why do we make page 0 and the pages between biosmem and ISA_HOLE_START
writeable in 2 maps?
- Which parts of vm86 and/or BIOSes need to write these pages?
- I think the non-FreeBSD part of vm86 needs to access (write?) page 0
in the vm86 map, so we must be mapping it there somewhere else. If
so, why do we handle it different to the other BIOS pages.
- Page 0 will need to be writeable in cpu_reset_real(), so the comment
which says that writeability is for vm86 will be incomplete. However,
r/w mapping could easily be delayed until it is needed in all cases.
- ISA_HOLE_START / PAGE_SIZE is sometimes hard-coded as 160.
- other points mentioned in comments.
Bruce
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