Re: [PATCH 1/4] x86 paravirt_ops: create no_paravirt.h for nativeops

From: Jeremy Fitzhardinge
Date: Mon Aug 07 2006 - 02:21:35 EST

Andi Kleen wrote:
so it would be nice to use one of the other serializing instructions in this case.

You would first need to find one that works in ring 3. On x86-64 it is used in the gettimeoday vsyscall in ring 3 to synchronize the TSC and afaik John was about to implement that for i386 too.

Well, that's really usermode code, so I don't think we'd necessarily touch it at all. It's not the same problem as the (single, at the moment) ring 0 use.

BTW another issue that I haven't checked but we will need to make
this also an alternative() for another case - it is faily important
to patch it out on Intel systems with a synchronized TSC where it is
fairly expensive. That is also not done yet on i386, but will be likely once vsyscall gettimeofday is implemented.

So basically you would need double patching. Ugly.

Yeah. I guess the cleanest way to do that is do the paravirt substitution, and then nop it out later if it isn't needed in the vsyscall.

I would recommend to keep it out of para ops.

It's hardly a big deal either way. There's only one in-kernel use of it.

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