Re: [PATCH] KVM: PPC: HV: Remove generic instruction emulation

[Alexander Graf <agraf@suse.de>]

On 30.07.14 18:21, Paolo Bonzini wrote:
> Il 30/07/2014 15:27, Alexander Graf ha scritto:
>> Now that we have properly split load/store instruction emulation and generic
>> instruction emulation, we can move the generic one from kvm.ko to kvm-pr.ko
>> on book3s_64.
>>
>> This reduces the attack surface and amount of code loaded on HV KVM kernels.
> Can emulation races happen on HV KVM like you can have on x86?
> Basically one CPU writes to MMIO while the other patches instructions so
> that basically anything can end up in the hands of the emulator?  On PPC
> it may even happen simply because of a missing icache invalidation, I
> think, since it doesn't support self-modifying code without explicit
> invalidation.

Yes, this is perfectly possible. As of my last patch set we will never 
enter the generic emulator for HV KVM, so that race is moot (we just 
inject a PROGRAM interrupt into the guest). With this patch even the 
code to emulate these bits doesn't exist in the kernel anymore if you 
don't modprobe kvm-pr.ko.


Alex