[Qemu-devel] CONFIG_QEMU patch

[Qemu-devel] CONFIG_QEMU patch

[Rusty Russell]

Hi all,

	Convenience patch for 2.5.74 (should apply to most 2.5
kernels) which adds a CONFIG_QEMU option.  This does all the frobbing
listed in the documentation, and also avoids a user access trap in
copy_mount_options() which OOPSes under QEMU.

This boots and runs for me, using the .config from vl-0.4.2.

Cheers,
Rusty.

Name: QEMU CONFIG Patch
Author: Rusty Russell
Status: Tested on 2.5.74-bk7

D: Convenient patch based on Fabrice Bellard's documentation on how to
D: boot an x86 kernel under qemu 0.4.  Adjusts PAGE_OFFSET, HZ, FIXADDR_TOP
D: and the arg copying code in namespace.c (which QEMU up to 0.4.2 doesn't
D: seem to handle correctly).

diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.74-bk7/arch/i386/Kconfig working-2.5.74-bk7-qemu-page-offset/arch/i386/Kconfig
--- linux-2.5.74-bk7/arch/i386/Kconfig	2003-07-10 10:55:41.000000000 +1000
+++ working-2.5.74-bk7-qemu-page-offset/arch/i386/Kconfig	2003-07-10 11:58:27.000000000 +1000
@@ -307,6 +307,14 @@ config X86_GENERIC
 	  when it has moderate overhead. This is intended for generic 
 	  distributions kernels.
 
+config QEMU
+	bool "Kernel to run under QEMU"
+	depends on EXPERIMENTAL
+	help
+	  Select this if you want to boot the kernel inside qemu, the
+	  x86 emulator.  See http://fabrice.bellard.free.fr/qemu/.
+	  Say N.
+
 #
 # Define implied options from the CPU selection here
 #
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.74-bk7/arch/i386/vmlinux.lds.S working-2.5.74-bk7-qemu-page-offset/arch/i386/vmlinux.lds.S
--- linux-2.5.74-bk7/arch/i386/vmlinux.lds.S	2003-06-15 11:29:47.000000000 +1000
+++ working-2.5.74-bk7-qemu-page-offset/arch/i386/vmlinux.lds.S	2003-07-10 11:58:27.000000000 +1000
@@ -3,14 +3,15 @@
  */
 
 #include <asm-generic/vmlinux.lds.h>
-	
+#include <asm/page.h>
+		
 OUTPUT_FORMAT("elf32-i386", "elf32-i386", "elf32-i386")
 OUTPUT_ARCH(i386)
 ENTRY(startup_32)
 jiffies = jiffies_64;
 SECTIONS
 {
-  . = 0xC0000000 + 0x100000;
+  . = __PAGE_OFFSET + 0x100000;
   /* read-only */
   _text = .;			/* Text and read-only data */
   .text : {
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.74-bk7/fs/namespace.c working-2.5.74-bk7-qemu-page-offset/fs/namespace.c
--- linux-2.5.74-bk7/fs/namespace.c	2003-07-10 10:55:46.000000000 +1000
+++ working-2.5.74-bk7-qemu-page-offset/fs/namespace.c	2003-07-10 15:05:22.000000000 +1000
@@ -676,7 +676,6 @@ out:
 
 static int copy_mount_options (const void __user *data, unsigned long *where)
 {
-	int i;
 	unsigned long page;
 	unsigned long size;
 	
@@ -687,22 +686,17 @@ static int copy_mount_options (const voi
 	if (!(page = __get_free_page(GFP_KERNEL)))
 		return -ENOMEM;
 
-	/* We only care that *some* data at the address the user
-	 * gave us is valid.  Just in case, we'll zero
-	 * the remainder of the page.
-	 */
-	/* copy_from_user cannot cross TASK_SIZE ! */
-	size = TASK_SIZE - (unsigned long)data;
-	if (size > PAGE_SIZE)
-		size = PAGE_SIZE;
+	size = strnlen_user(data, PAGE_SIZE-1);
+	if (size == 0) {
+		free_page(page); 
+		return -EFAULT;
+	}
 
-	i = size - copy_from_user((void *)page, data, size);
-	if (!i) {
+	if (copy_from_user((void *)page, data, size) != 0) {
 		free_page(page); 
 		return -EFAULT;
 	}
-	if (i != PAGE_SIZE)
-		memset((char *)page + i, 0, PAGE_SIZE - i);
+	memset((char *)page + size, 0, PAGE_SIZE - size);
 	*where = page;
 	return 0;
 }
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.74-bk7/include/asm-i386/fixmap.h working-2.5.74-bk7-qemu-page-offset/include/asm-i386/fixmap.h
--- linux-2.5.74-bk7/include/asm-i386/fixmap.h	2003-06-15 11:30:06.000000000 +1000
+++ working-2.5.74-bk7-qemu-page-offset/include/asm-i386/fixmap.h	2003-07-10 11:58:27.000000000 +1000
@@ -100,7 +100,11 @@ extern void __set_fixmap (enum fixed_add
  * Leave one empty page between vmalloc'ed areas and
  * the start of the fixmap.
  */
+#ifdef CONFIG_QEMU
+#define FIXADDR_TOP	(0xa7fff000UL)
+#else
 #define FIXADDR_TOP	(0xfffff000UL)
+#endif
 #define __FIXADDR_SIZE	(__end_of_permanent_fixed_addresses << PAGE_SHIFT)
 #define FIXADDR_START	(FIXADDR_TOP - __FIXADDR_SIZE)
 
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.74-bk7/include/asm-i386/page.h working-2.5.74-bk7-qemu-page-offset/include/asm-i386/page.h
--- linux-2.5.74-bk7/include/asm-i386/page.h	2003-04-08 11:14:55.000000000 +1000
+++ working-2.5.74-bk7-qemu-page-offset/include/asm-i386/page.h	2003-07-10 11:58:27.000000000 +1000
@@ -10,10 +10,10 @@
 #define LARGE_PAGE_SIZE (1UL << PMD_SHIFT)
 
 #ifdef __KERNEL__
-#ifndef __ASSEMBLY__
-
 #include <linux/config.h>
 
+#ifndef __ASSEMBLY__
+
 #ifdef CONFIG_X86_USE_3DNOW
 
 #include <asm/mmx.h>
@@ -115,12 +115,19 @@ static __inline__ int get_order(unsigned
 #endif /* __ASSEMBLY__ */
 
 #ifdef __ASSEMBLY__
+#ifdef CONFIG_QEMU
+#define __PAGE_OFFSET		(0x90000000)
+#else
 #define __PAGE_OFFSET		(0xC0000000)
+#endif /* QEMU */
+#else
+#ifdef CONFIG_QEMU
+#define __PAGE_OFFSET		(0x90000000UL)
 #else
 #define __PAGE_OFFSET		(0xC0000000UL)
+#endif /* QEMU */
 #endif
 
-
 #define PAGE_OFFSET		((unsigned long)__PAGE_OFFSET)
 #define VMALLOC_RESERVE		((unsigned long)__VMALLOC_RESERVE)
 #define MAXMEM			(-__PAGE_OFFSET-__VMALLOC_RESERVE)
diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal linux-2.5.74-bk7/include/asm-i386/param.h working-2.5.74-bk7-qemu-page-offset/include/asm-i386/param.h
--- linux-2.5.74-bk7/include/asm-i386/param.h	2003-01-02 12:07:44.000000000 +1100
+++ working-2.5.74-bk7-qemu-page-offset/include/asm-i386/param.h	2003-07-10 11:58:27.000000000 +1000
@@ -2,7 +2,12 @@
 #define _ASMi386_PARAM_H
 
 #ifdef __KERNEL__
-# define HZ		1000		/* Internal kernel timer frequency */
+# include <linux/config.h>
+# ifdef CONFIG_QEMU
+#  define HZ		100
+# else
+#  define HZ		1000		/* Internal kernel timer frequency */
+# endif
 # define USER_HZ	100		/* .. some user interfaces are in "ticks" */
 # define CLOCKS_PER_SEC	(USER_HZ)	/* like times() */
 #endif

--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: [Qemu-devel] CONFIG_QEMU patch

[David S. Miller]

   From: Rusty Russell <rusty@rustcorp.com.au>
   Date: Thu, 10 Jul 2003 15:46:24 +1000
   
   and also avoids a user access trap in
   copy_mount_options() which OOPSes under QEMU.

Is this a bug in this kernel code or a QEMU issue?

Re: [Qemu-devel] CONFIG_QEMU patch

[Rusty Russell]

In message <20030709.230357.91335242.davem@redhat.com> you write:
>    From: Rusty Russell <rusty@rustcorp.com.au>
>    Date: Thu, 10 Jul 2003 15:46:24 +1000
>    
>    and also avoids a user access trap in
>    copy_mount_options() which OOPSes under QEMU.
> 
> Is this a bug in this kernel code or a QEMU issue?

QEMU, definitely.  copy_mount_options() is the only place where the
copy_from_user regularly fails.  That's mainly because it's bad code,
but it's a useful canary for exactly this readson.

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.