Re: [PATCH] KVM: handle exit due to INVD in VMX

[Alexander Graf <agraf@suse.de>]

On 31.10.2010, at 11:56, Gleb Natapov wrote:

> On Sun, Oct 31, 2010 at 11:26:09AM -0700, Alexander Graf wrote:
>> 
>> On 31.10.2010, at 11:22, Gleb Natapov wrote:
>> 
>>> On Sun, Oct 31, 2010 at 11:00:08AM -0700, Alexander Graf wrote:
>>>> 
>>>> On 31.10.2010, at 07:36, Gleb Natapov wrote:
>>>> 
>>>>> Call into emulator when INVD instruction is executed by a guest.
>>>> 
>>>> Why? This is a poor patch description.
>>> Why what? Why we need to handle INVD exit instead of stopping with
>>> unhandled exit error?
>> 
>> Ah, so we get the exit already, but don't handle it? That's an important piece of information that belongs in the patch description. Another thing I as a reader would also like to know is where this got triggered, so which guests would break without the patch.
>> 
> I'll add it to the patch description. The guest that triggered it was
> open firmware, but I do not think this info belongs to patch description
> too.

Quite the contrary, I would be very interested in that information in the patch description. The patch description is what people afterwards use to cherry-pick patches. So this is crucial.

> 
>> I'm also wondering why nobody has seen it before. Is this a regression? Is this exit a side-effect of another feature bit of VMX, so only newer CPUs are affected?
>> 
> I guess nobody seen it because not many guests use the instruction.
> Actually this instruction is useful only for firmware use. This is not a
> regression.

This, too, should go in the patch description :). At least the part that usually only firmware uses it. The part where it has been around since the beginning might be interesting as well from a security point of view. After all, the guest can kill its full kvm context without going through qemu interfaces.


Thanks!

Alex