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Date: Tue, 25 Aug 2009 21:03:19 +0300
From: Pekka Enberg <penberg@...helsinki.fi>
To: Arnd Hannemann <hannemann@...s.rwth-aachen.de>
Cc: Arnd Hannemann <Arnd.Hannemann@...s.rwth-aachen.de>,
LKML <linux-kernel@...r.kernel.org>,
"hannes@...xchg.org" <hannes@...xchg.org>,
"torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
Jeremy Fitzhardinge <jeremy@...p.org>,
"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
Ingo Molnar <mingo@...e.hu>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [bisected] 2.6.31 regression: fails to boot as xen guest
On Tue, 2009-08-25 at 19:49 +0200, Arnd Hannemann wrote:
> Hi Pekka,
>
> Pekka Enberg wrote:
> > On Tue, 2009-08-25 at 18:49 +0200, Arnd Hannemann wrote:
> >>> Thanks for doing the bisect! Can we also see your .config also?
> >> Config for -rc7 is attached. My bisect configs were based on that
> >
> > Thanks! While we wait for the Xen people, you can try the following
> > patch to see if we can narrow the bug down to trap_init().
>
> Yes seems to be trap_init().
> -rc7 with this patch applied boots up to the prompt.
Thanks for testing! Ingo, what do you think of the following patch?
AFAICT, x86-32 is the only architecture playing with traps in mem_init()
so this should be the safest fix for 2.6.31.
Pekka
>>From b739e3c3baa6312664b4ea676bdf73df27fcecbc Mon Sep 17 00:00:00 2001
From: Pekka Enberg <penberg@...helsinki.fi>
Date: Tue, 25 Aug 2009 20:55:25 +0300
Subject: [PATCH] x86: Move WP bit testing to trap_init()
Commit 83b519e8b9572c319c8e0c615ee5dd7272856090 ("slab: setup allocators
earlier in the boot sequence") moved trap_init() earlier in the boot
sequence to avoid a hard crash with 32-bit x86 in mem_init().
Unfortunately the change broke Xen so make trap_init() later and move
the WP bit test from mem_init() to trap_init().
Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
---
arch/x86/kernel/traps.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++
arch/x86/mm/init_32.c | 56 ----------------------------------------------
init/main.c | 2 +-
3 files changed, 58 insertions(+), 57 deletions(-)
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 5204332..2084408 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -906,6 +906,60 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
return;
do_trap(32, SIGILL, "iret exception", regs, error_code, &info);
}
+
+static noinline int do_test_wp_bit(void);
+
+/*
+ * Test if the WP bit works in supervisor mode. It isn't supported on 386's
+ * and also on some strange 486's. All 586+'s are OK. This used to involve
+ * black magic jumps to work around some nasty CPU bugs, but fortunately the
+ * switch to using exceptions got rid of all that.
+ */
+static void __init test_wp_bit(void)
+{
+ printk(KERN_INFO
+ "Checking if this processor honours the WP bit even in supervisor mode...");
+
+ /* Any page-aligned address will do, the test is non-destructive */
+ __set_fixmap(FIX_WP_TEST, __pa(&swapper_pg_dir), PAGE_READONLY);
+ boot_cpu_data.wp_works_ok = do_test_wp_bit();
+ clear_fixmap(FIX_WP_TEST);
+
+ if (!boot_cpu_data.wp_works_ok) {
+ printk(KERN_CONT "No.\n");
+#ifdef CONFIG_X86_WP_WORKS_OK
+ panic(
+ "This kernel doesn't support CPU's with broken WP. Recompile it for a 386!");
+#endif
+ } else {
+ printk(KERN_CONT "Ok.\n");
+ }
+}
+
+/*
+ * This function cannot be __init, since exceptions don't work in that
+ * section. Put this after the callers, so that it cannot be inlined.
+ */
+static noinline int do_test_wp_bit(void)
+{
+ char tmp_reg;
+ int flag;
+
+ __asm__ __volatile__(
+ " movb %0, %1 \n"
+ "1: movb %1, %0 \n"
+ " xorl %2, %2 \n"
+ "2: \n"
+ _ASM_EXTABLE(1b,2b)
+ :"=m" (*(char *)fix_to_virt(FIX_WP_TEST)),
+ "=q" (tmp_reg),
+ "=r" (flag)
+ :"2" (1)
+ :"memory");
+
+ return flag;
+}
+
#endif
void __init trap_init(void)
@@ -982,5 +1036,8 @@ void __init trap_init(void)
#ifdef CONFIG_X86_32
x86_quirk_trap_init();
+
+ if (boot_cpu_data.wp_works_ok < 0)
+ test_wp_bit();
#endif
}
diff --git a/arch/x86/mm/init_32.c b/arch/x86/mm/init_32.c
index 3cd7711..e22bb8a 100644
--- a/arch/x86/mm/init_32.c
+++ b/arch/x86/mm/init_32.c
@@ -54,8 +54,6 @@
unsigned long highstart_pfn, highend_pfn;
-static noinline int do_test_wp_bit(void);
-
bool __read_mostly __vmalloc_start_set = false;
static __init void *alloc_low_page(void)
@@ -830,33 +828,6 @@ void __init paging_init(void)
zone_sizes_init();
}
-/*
- * Test if the WP bit works in supervisor mode. It isn't supported on 386's
- * and also on some strange 486's. All 586+'s are OK. This used to involve
- * black magic jumps to work around some nasty CPU bugs, but fortunately the
- * switch to using exceptions got rid of all that.
- */
-static void __init test_wp_bit(void)
-{
- printk(KERN_INFO
- "Checking if this processor honours the WP bit even in supervisor mode...");
-
- /* Any page-aligned address will do, the test is non-destructive */
- __set_fixmap(FIX_WP_TEST, __pa(&swapper_pg_dir), PAGE_READONLY);
- boot_cpu_data.wp_works_ok = do_test_wp_bit();
- clear_fixmap(FIX_WP_TEST);
-
- if (!boot_cpu_data.wp_works_ok) {
- printk(KERN_CONT "No.\n");
-#ifdef CONFIG_X86_WP_WORKS_OK
- panic(
- "This kernel doesn't support CPU's with broken WP. Recompile it for a 386!");
-#endif
- } else {
- printk(KERN_CONT "Ok.\n");
- }
-}
-
static struct kcore_list kcore_mem, kcore_vmalloc;
void __init mem_init(void)
@@ -956,9 +927,6 @@ void __init mem_init(void)
BUG_ON(VMALLOC_START >= VMALLOC_END);
BUG_ON((unsigned long)high_memory > VMALLOC_START);
- if (boot_cpu_data.wp_works_ok < 0)
- test_wp_bit();
-
save_pg_dir();
zap_low_mappings(true);
}
@@ -975,30 +943,6 @@ int arch_add_memory(int nid, u64 start, u64 size)
}
#endif
-/*
- * This function cannot be __init, since exceptions don't work in that
- * section. Put this after the callers, so that it cannot be inlined.
- */
-static noinline int do_test_wp_bit(void)
-{
- char tmp_reg;
- int flag;
-
- __asm__ __volatile__(
- " movb %0, %1 \n"
- "1: movb %1, %0 \n"
- " xorl %2, %2 \n"
- "2: \n"
- _ASM_EXTABLE(1b,2b)
- :"=m" (*(char *)fix_to_virt(FIX_WP_TEST)),
- "=q" (tmp_reg),
- "=r" (flag)
- :"2" (1)
- :"memory");
-
- return flag;
-}
-
#ifdef CONFIG_DEBUG_RODATA
const int rodata_test_data = 0xC3;
EXPORT_SYMBOL_GPL(rodata_test_data);
diff --git a/init/main.c b/init/main.c
index 2d9d6bd..5c4dacb 100644
--- a/init/main.c
+++ b/init/main.c
@@ -603,7 +603,6 @@ asmlinkage void __init start_kernel(void)
pidhash_init();
vfs_caches_init_early();
sort_main_extable();
- trap_init();
mm_init();
/*
* Set up the scheduler prior starting any interrupts (such as the
@@ -621,6 +620,7 @@ asmlinkage void __init start_kernel(void)
"enabled *very* early, fixing it\n");
local_irq_disable();
}
+ trap_init();
rcu_init();
/* init some links before init_ISA_irqs() */
early_irq_init();
--
1.5.6.3
--
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