[PATCH 3/6] KVM: PPC: Book3E: Increase FPU laziness

[Alexander Graf]

On 03.07.2013, at 15:55, Caraman Mihai Claudiu-B02008 wrote:

>> -----Original Message-----
>> From: Alexander Graf [mailto:agraf at suse.de]
>> Sent: Wednesday, July 03, 2013 4:45 PM
>> To: Caraman Mihai Claudiu-B02008
>> Cc: kvm-ppc at vger.kernel.org; kvm at vger.kernel.org; linuxppc-
>> dev at lists.ozlabs.org
>> Subject: Re: [PATCH 3/6] KVM: PPC: Book3E: Increase FPU laziness
>> 
>> 
>> On 03.07.2013, at 14:42, Mihai Caraman wrote:
>> 
>>> Increase FPU laziness by calling kvmppc_load_guest_fp() just before
>>> returning to guest instead of each sched in. Without this improvement
>>> an interrupt may also claim floting point corrupting guest state.
>> 
>> Not sure I follow. Could you please describe exactly what's happening?
> 
> This was already discussed on the list, I will forward you the thread.

The only thing I've seen in that thread was some pathetic theoretical case where an interrupt handler would enable fp and clobber state carelessly. That's not something I'm worried about.

I really don't see where this patch improves anything tbh. It certainly makes the code flow more awkward.


Alex