[Lguest] [PATCH] fix lguest rmmod "bad pgd"

Rusty Russell rusty at rustcorp.com.au
Tue Jan 1 21:48:36 EST 2008


After 17d57a9206b4de6ad082ac9f2d2346985abbd2aa
(x86: fix x86-32 early fixmap initialization.) removing lg.ko caused a printk
from vunmap:

	mm/memory.c:115: bad pgd 004b3027.

On the second use after module load, the kernel crashes.

This fixes the immediate problem (accessed and dirty bits not set as
expected in pmd_none_or_clear_bad).  I can't see why this would cause
a crash, but I haven't been able to reproduce it once this is applied.

Signed-off-by: Rusty Russell <rusty at rustcorp.com.au>

diff --git a/arch/x86/kernel/head_32.S b/arch/x86/kernel/head_32.S
--- a/arch/x86/kernel/head_32.S
+++ b/arch/x86/kernel/head_32.S
@@ -196,7 +196,7 @@ 11:
 	/* Do an early initialization of the fixmap area */
 	movl $(swapper_pg_dir - __PAGE_OFFSET), %edx
 	movl $(swapper_pg_pmd - __PAGE_OFFSET), %eax
-	addl $0x007, %eax			/* 0x007 = PRESENT+RW+USER */
+	addl $0x67, %eax			/* 0x67 == _PAGE_TABLE */
 	movl %eax, 4092(%edx)
 
 	xorl %ebx,%ebx				/* This is the boot CPU (BSP) */



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