[PATCH] x86/32: skip early initialisation of swapper_pg_dir if it is already current

[Ian Campbell]

In particular in the Xen PV case the Xen early startup code has
already initialised swapper_pg_dir and switched to it. In this case
initial_page_table is uninitialised since Xen has no use for it so
copying it over swapper_pg_dir is not correct.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
---
 arch/x86/kernel/setup.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
index 95a3274..2d89d5a 100644
--- a/arch/x86/kernel/setup.c
+++ b/arch/x86/kernel/setup.c
@@ -705,12 +705,14 @@ void __init setup_arch(char **cmdline_p)
 	 * copy kernel address range established so far and switch
 	 * to the proper swapper page table
 	 */
-	clone_pgd_range(swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
-			initial_page_table + KERNEL_PGD_BOUNDARY,
-			KERNEL_PGD_PTRS);
+	if (read_cr3() != __pa(swapper_pg_dir)) {
+		clone_pgd_range(swapper_pg_dir     + KERNEL_PGD_BOUNDARY,
+				initial_page_table + KERNEL_PGD_BOUNDARY,
+				KERNEL_PGD_PTRS);
 
-	load_cr3(swapper_pg_dir);
-	__flush_tlb_all();
+		load_cr3(swapper_pg_dir);
+		__flush_tlb_all();
+	}
 #else
 	printk(KERN_INFO "Command line: %s\n", boot_command_line);
 #endif
-- 
1.5.6.5



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