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

[Mikael Pettersson]

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.

/Mikael
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