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Date: Fri, 4 Jan 2008 13:00:36 -0500
From: Jeff Dike <jdike@...toit.com>
To: Miklos Szeredi <miklos@...redi.hu>
Cc: akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: [uml-devel] UML woes in 2.6.24-rc6-mm1
On Thu, Jan 03, 2008 at 01:55:57PM +0100, Miklos Szeredi wrote:
> This is the one: uml-runtime-detection-of-host-vmsplit-on-i386.patch
>
> The relevant log line (both for successful and failed boots):
>
> Locating the top of the address space ... 0xffc00000
Thanks for narrowing it down. It turns out I can reproduce it with a
defconfig, but it reproduces much more easily with your config for
some reason.
Anyhow, try the patch below.
Jeff
--
Work email - jdike at linux dot intel dot com
Index: linux-2.6.22/arch/um/include/as-layout.h
===================================================================
--- linux-2.6.22.orig/arch/um/include/as-layout.h 2008-01-01 17:32:04.000000000 -0500
+++ linux-2.6.22/arch/um/include/as-layout.h 2008-01-04 12:27:21.000000000 -0500
@@ -57,6 +57,8 @@ extern unsigned long _stext, _etext, _sd
extern unsigned long _unprotected_end;
extern unsigned long brk_start;
+extern unsigned long host_task_size;
+
extern int linux_main(int argc, char **argv);
extern void (*sig_info[])(int, struct uml_pt_regs *);
Index: linux-2.6.22/arch/um/kernel/exec.c
===================================================================
--- linux-2.6.22.orig/arch/um/kernel/exec.c 2008-01-04 12:12:32.000000000 -0500
+++ linux-2.6.22/arch/um/kernel/exec.c 2008-01-04 12:27:48.000000000 -0500
@@ -25,7 +25,7 @@ void flush_thread(void)
ret = unmap(¤t->mm->context.id, 0, STUB_START, 0, &data);
ret = ret || unmap(¤t->mm->context.id, STUB_END,
- TASK_SIZE - STUB_END, 1, &data);
+ host_task_size - STUB_END, 1, &data);
if (ret) {
printk(KERN_ERR "flush_thread - clearing address space failed, "
"err = %d\n", ret);
Index: linux-2.6.22/arch/um/kernel/um_arch.c
===================================================================
--- linux-2.6.22.orig/arch/um/kernel/um_arch.c 2008-01-04 12:11:33.000000000 -0500
+++ linux-2.6.22/arch/um/kernel/um_arch.c 2008-01-04 12:53:53.000000000 -0500
@@ -244,6 +244,8 @@ static struct notifier_block panic_exit_
unsigned long task_size;
EXPORT_SYMBOL(task_size);
+unsigned long host_task_size;
+
unsigned long brk_start;
unsigned long end_iomem;
EXPORT_SYMBOL(end_iomem);
@@ -270,11 +272,12 @@ int __init linux_main(int argc, char **a
if (have_root == 0)
add_arg(DEFAULT_COMMAND_LINE);
+ host_task_size = os_get_task_size();
/*
* TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps
* out
*/
- task_size = os_get_task_size(PGDIR_SHIFT);
+ task_size = host_task_size & PGDIR_MASK;
/* OS sanity checks that need to happen before the kernel runs */
os_early_checks();
Index: linux-2.6.22/arch/um/os-Linux/sys-i386/task_size.c
===================================================================
--- linux-2.6.22.orig/arch/um/os-Linux/sys-i386/task_size.c 2008-01-01 17:32:04.000000000 -0500
+++ linux-2.6.22/arch/um/os-Linux/sys-i386/task_size.c 2008-01-04 12:56:20.000000000 -0500
@@ -49,7 +49,7 @@ static int page_ok(unsigned long page)
ok = 1;
goto out;
} else if (mprotect(address, UM_KERN_PAGE_SIZE,
- PROT_READ | PROT_WRITE) != 0)
+ PROT_READ | PROT_WRITE) != 0)
goto out;
if (setjmp(buf) == 0) {
@@ -63,13 +63,20 @@ static int page_ok(unsigned long page)
return ok;
}
-unsigned long os_get_task_size(int shift)
+unsigned long os_get_task_size(void)
{
struct sigaction sa, old;
- unsigned long bottom = 0 >> shift;
- unsigned long top = ~0UL >> shift;
+ unsigned long bottom = 0;
+ /*
+ * A 32-bit UML on a 64-bit host gets confused about the VDSO at
+ * 0xffffe000. It is mapped, is readable, can be reprotected writeable
+ * and written. However, exec discovers later that it can't be
+ * unmapped. So, just set the highest address to be checked to just
+ * below it. This might waste some address space on 4G/4G 32-bit
+ * hosts, but shouldn't hurt otherwise.
+ */
+ unsigned long top = 0xffffd000 >> UM_KERN_PAGE_SHIFT;
unsigned long test;
- int to_page = shift - UM_KERN_PAGE_SHIFT;
printf("Locating the top of the address space ... ");
fflush(stdout);
@@ -83,18 +90,19 @@ unsigned long os_get_task_size(int shift
sa.sa_flags = SA_NODEFER;
sigaction(SIGSEGV, &sa, &old);
- if (!page_ok(bottom << to_page)) {
- fprintf(stderr, "Address 0x%x no good?\n", bottom << shift);
+ if (!page_ok(bottom)) {
+ fprintf(stderr, "Address 0x%x no good?\n",
+ bottom << UM_KERN_PAGE_SHIFT);
exit(1);
}
/* This could happen with a 4G/4G split */
- if (page_ok(top << to_page))
+ if (page_ok(top))
goto out;
do {
test = bottom + (top - bottom) / 2;
- if (page_ok(test << to_page))
+ if (page_ok(test))
bottom = test;
else
top = test;
@@ -104,7 +112,9 @@ out:
/* Restore the old SIGSEGV handling */
sigaction(SIGSEGV, &old, NULL);
- printf("0x%x\n", top << shift);
+ top <<= UM_KERN_PAGE_SHIFT;
+ printf("0x%x\n", top);
fflush(stdout);
- return top << shift;
+
+ return top;
}
Index: linux-2.6.22/arch/um/include/os.h
===================================================================
--- linux-2.6.22.orig/arch/um/include/os.h 2008-01-04 12:55:38.000000000 -0500
+++ linux-2.6.22/arch/um/include/os.h 2008-01-04 12:55:48.000000000 -0500
@@ -299,6 +299,6 @@ extern int os_arch_prctl(int pid, int co
extern int get_pty(void);
/* sys-$ARCH/task_size.c */
-extern unsigned long os_get_task_size(int shift);
+extern unsigned long os_get_task_size(void);
#endif
--
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