Virtualization - Apr 2007 - [PATCH] Fix potential interrupts during alternative patching [was Re: [RFC] Avoid PIT SMP lockups]

On Thu, Oct 19, 2006 at 01:00:55AM -0700, Zachary Amsden
wrote:
> S.??a??lar Onur wrote:
> >17 Eki 2006 Sal 01:21 tarihinde, S.??a??lar Onur ??unlar?? yazm????t??:
> >  
> >>17 Eki 2006 Sal 01:17 tarihinde, Zachary Amsden ??unlar??
yazm????t??:
> >>    
> >>>My nasty quick patch might not apply - the only tree I've
got is a very
> >>>hacked 2.6.18-rc6-mm1+local-patches thing, but the fix should
be obvious
> >>>enough.
> >>>      
> >>Ok, I'll test and report back...
> >>    
> >
> >Both 2.6.18 and 2.6.18.1 boots without any problem (and of course
without
> >noreplacement workarund) with that patch.
> >
> >Cheers
> >  
> 
> So this patch is an obvious bugfix - please apply, and to stable as 
> well. I'm not sure when this broke, but taking interrupts in the middle
> of self modifying code is not a pretty sight.
Please send -stable patches to stable@kernel.org, not to me directly (we
are a team and hand off ownership to each other, by sending it to the
alias it makes sure that nothing gets lots in our individual mail
boxes.)

Also, please let stable know when this is upstream, we don't want to
apply it before then.

thanks,

greg k-h

S.Çağlar Onur wrote:
> 17 Eki 2006 Sal 01:21 tarihinde, S.Çağlar Onur şunları yazmıştı: 
>   
>> 17 Eki 2006 Sal 01:17 tarihinde, Zachary Amsden şunları yazmıştı:
>>     
>>> My nasty quick patch might not apply - the only tree I've got
is a very
>>> hacked 2.6.18-rc6-mm1+local-patches thing, but the fix should be
obvious
>>> enough.
>>>       
>> Ok, I'll test and report back...
>>     
>
> Both 2.6.18 and 2.6.18.1 boots without any problem (and of course without 
> noreplacement workarund) with that patch.
>
> Cheers
>   
So this patch is an obvious bugfix - please apply, and to stable as 
well. I'm not sure when this broke, but taking interrupts in the middle 
of self modifying code is not a pretty sight.

Zach
-------------- next part --------------
Interrupts must be disabled during alternative instruction patching.
On systems with high timer IRQ rates, or when running in an emulator,
timing differences can result in random kernel panics because of
running partially patched instructions.  This doesn't yet fix NMIs,
which requires extricating the patch code from the late bug checking
and is logically separate (and also less likely to cause problems).

Signed-off-by: Zachary Amsden <zach@vmware.com>


diff -r 773ac0ebfeb4 arch/i386/kernel/alternative.c
--- a/arch/i386/kernel/alternative.c	Wed Oct 18 06:03:56 2006 -0700
+++ b/arch/i386/kernel/alternative.c	Wed Oct 18 06:07:03 2006 -0700
@@ -344,6 +344,7 @@ void alternatives_smp_switch(int smp)
 
 void __init alternative_instructions(void)
 {
+	unsigned long flags;
 	if (no_replacement) {
 		printk(KERN_INFO "(SMP-)alternatives turned off\n");
 		free_init_pages("SMP alternatives",
@@ -351,6 +352,8 @@ void __init alternative_instructions(voi
 				(unsigned long)__smp_alt_end);
 		return;
 	}
+
+	local_irq_save(flags);
 	apply_alternatives(__alt_instructions, __alt_instructions_end);
 
 	/* switch to patch-once-at-boottime-only mode and free the
@@ -386,4 +389,5 @@ void __init alternative_instructions(voi
 		alternatives_smp_switch(0);
 	}
 #endif
-}
+	local_irq_restore(flags);
+}

Zachary Amsden wrote:
> So this patch is an obvious bugfix - please apply, and to stable as 
> well. I'm not sure when this broke, but taking interrupts in the 
> middle of self modifying code is not a pretty sight.
I had actually seen this when I built the Xen paravirt kernel with SMP 
on, but I assumed it was something in the pv_ops tree rather than 
mainline...

    J