linux-kernel - Re: [PATCH] x86: use pgd accessors when cloning a pgd range.

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Date:	Thu, 28 Oct 2010 10:23:17 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Borislav Petkov <bp@...en8.de>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86: use pgd accessors when cloning a pgd range.

On Wed, 2010-10-27 at 18:58 +0100, Ian Campbell wrote:
> I think we could achieve this within the Xen pvops backend but e.g.
> the following would likely work also.
> 
> (Note, untested. I also omitted the reindent for clarity at this
> point)

Now tested and it works. Patch below.

I'm also going to look into switching Xen to startup on
initial_page_table, since I think the consistency with native would be
useful from a principle of least surprise PoV. However the following is
a useful stopgap if nothing else.

BTW, are there plans to unify 32 and 64 bit WRT the use of
swapper_pg_dir vs initial_page_table?

Ian.

8<-------------------------

>From 9bbce2e6b198cc7efeeebb87131e5b4e9ac923bd Mon Sep 17 00:00:00 2001
From: Ian Campbell <ian.campbell@...rix.com>
Date: Thu, 28 Oct 2010 10:16:52 +0100
Subject: [PATCH] x86/32: skip early initialisation of swapper_pg_dir if it is already current

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@...rix.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: H. Peter Anvin <hpa@...ux.intel.com>
Cc: Jeremy Fitzhardinge <jeremy@...p.org>
---
 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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