Re: [PATCH][uq/master] kvm: x86: Save/restore FPU OP, IP and DP

Avi Kivity
2011-06-15T11:26:33Z

On 06/15/2011 01:20 PM, Jan Kiszka wrote:
> >
> > So fopcode will usually be clear.
> >
>
> OK. So if bit 2 of IA32_MISC_ENABLE MSR, we must save that fields. But
> if it's off, how to test for that other condition "last non-transparent
> FP instruction ... had an unmasked exception" from the host?
>

We save fopcode unconditionally. But if IA32_MISC_ENABLE_MSR[2]=0, then
fopcode will be zero, and we can skip the subsection (if the data and
instruction pointers are also zero, which they will be).

If it isn't zero, there's still a good chance fopcode will be zero
(64-bit userspace, thread that hasn't used the fpu since the last
context switch, last opcode happened to be zero).

--
error compiling committee.c: too many arguments to function