Messages in this thread | | | Date | Tue, 19 Sep 2006 20:52:55 -0400 | From | Karim Yaghmour <> | Subject | Re: [PATCH] Linux Kernel Markers |
| |
Alan Cox wrote: > Ar Maw, 2006-09-19 am 13:54 -0400, ysgrifennodd Mathieu Desnoyers: >> Very good idea.. However, overwriting the second instruction with a jump could >> be dangerous on preemptible and SMP kernels, because we never know if a thread >> has an IP in any of its contexts that would return exactly at the middle of the >> jump. > > No: on x86 it is the *same* case for all of these even writing an int3. > One byte or a megabyte, > > You MUST ensure that every CPU executes a serializing instruction before > it hits code that was modified by another processor. Otherwise you get > CPU errata and the CPU produces results which vendors like to describe > as "undefined".
I was aware of that this errata existed, but never actually knew the actual specifics of it. Are these two separate problems or just one? a) the errata & a possible thread having an IP leading back within (not at the start of) the range to be replaced. b) the errata & replacing single instruction with single instruction of same size.
In a), there's almost an intractable problem of making sure no IP leads back within the range to be replaced. In b) we still have to take care of the errata part, but no worry about the stalled thread with invalid IP.
> Thus you have to serialize, and if you are serializing it really doesn't > matter if you write a byte, a paragraph or a page.
I was vaguely aware of the issue on x86. Do you know if this applies the same on other achitectures?
Also, this is SMP-only, right? (Not that single UP matters for desktop anymore, but just checking.)
Any pointers to the errata?
Karim -- President / Opersys Inc. Embedded Linux Training and Expertise www.opersys.com / 1.866.677.4546 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |