Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

From: Mikael Pettersson
Date: Thu May 22 2008 - 04:51:31 EST

Roland McGrath writes:
> > The biggest potential problem with this that I see is that relying on
> > CPUID can mess with certain virtualization solutions. Another option to
> > accomplish the same thing would be to have a system call (preferrably a
> > prctl, since it is at least in theory personality-dependent) to query
> > what information is included in the fpstate data - since it will always
> > be the same for any particular kernel.
> It's easy and cheap to add an indicator to the vDSO for this.

For our user-space virtualisation code a plain system call,
like prctl(), would be strongly preferable. Right now I
can't say whether a vDSO solution would work at all for us,
but a system call solution would be no problem at all.

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