Re: [patch] SMP alternatives

From: Andi Kleen
Date: Wed Nov 23 2005 - 13:46:23 EST

On Wed, Nov 23, 2005 at 10:42:40AM -0800, Linus Torvalds wrote:
> On Wed, 23 Nov 2005, H. Peter Anvin wrote:
> >
> > Linus Torvalds wrote:
> > > What I suggested to Intel at the Developer Days is to have a MSR (or, better
> > > yet, a bit in the page table pointer %cr0) that disables "lock" in _user_
> > > space. Ie a lock would be a no-op when in CPL3, and only with certain
> > > processes.
> >
> > You mean %cr3, right?
> Yes.
> It _should_ be fairly easy to do something like that - just a simple
> global flag that gets set and makes CPL3 ignore lock prefixes. Even timing
> doesn't matter - it it takes a hundred cycles for the setting to take
> effect, we don't care, since you can't write %cr3 from user space anyway,
> and it will certainly take a hundred cycles (and a few serializing
> instructions) until we get to CPL3.

Another bit for ring 0 would be actually useful too. Then the patching
patch here wouldn't be needed.

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