[PATCH] i386: clear_fixmap() should not use set_pte()

["Jan Beulich" <jbeulich@novell.com>]

While not strictly required with the current code (as the upper half of
page table entries generated by __set_fixmap() cannot be non-zero due
to the second parameter of this function being 'unsigned long'), the
use of set_pte() in __set_fixmap() in the context of clear_fixmap() is
still improper with CONFIG_X86_PAE (see the respective comment in
include/asm-i386/pgtable-3level.h) and would turn into a bug if that
second parameter ever gets changed to a 64-bit type.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

--- linux-2.6.19-rc5/arch/i386/mm/pgtable.c	2006-11-08 09:21:37.000000000 +0100
+++ 2.6.19-rc5-i386-clear_fixmap/arch/i386/mm/pgtable.c	2006-11-06 12:13:29.000000000 +0100
@@ -95,8 +95,11 @@ static void set_pte_pfn(unsigned long va
 		return;
 	}
 	pte = pte_offset_kernel(pmd, vaddr);
-	/* <pfn,flags> stored as-is, to permit clearing entries */
-	set_pte(pte, pfn_pte(pfn, flags));
+	if (pgprot_val(flags))
+		/* <pfn,flags> stored as-is, to permit clearing entries */
+		set_pte(pte, pfn_pte(pfn, flags));
+	else
+		pte_clear(&init_mm, vaddr, pte);
 
 	/*
 	 * It's enough to flush this one mapping.