Re: [Xen-devel] Status of VM event patches (Was: Re: Xen 4.6 Development Update (2 WEEKS TO FREEZE, important information in preamble))

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jun 26, 2015 at 06:23:02PM +0300, Razvan Cojocaru wrote:
> On 06/26/2015 02:16 PM, wei.liu2@xxxxxxxxxx wrote:
> > *  VM event patches (none)
> >    Add support for XSETBV vm_events,
> >    Support hybernating guests
> >    Support for VMCALL-based vm_events
> >   -  Razvan Cojocaru
> 
> Since V2, there are now 3 more patches that we'd like to see in Xen
> mainline at some point:
> 
> 1. The patch we've originally submitted that computed the current
> instruction length in order to be able to skip it completely (instead of
> emulating it with dummy nop write operations) has been somewhat
> controversial. To that end, we're now computing the instruction length
> in the userspace application, and simply send the new EIP back to the HV
> in the vm_event reply, so that skipping instructions can work without a
> lot of code added to Xen.
> 
> 2. In the past, we've aways disabled REP optimizations (forcing *reps to
> 1) when introspection is active. Tamas' work now gates this on
> current->domain->arch.mem_access_emulate_enabled in
> xen/arch/x86/hvm/emulate.c. A side effect of that is that Windows HVM
> guests tend to boot much slower. We'd like to add a dedicated libxc
> function that enables / disables this pessimization explicitly.
> 
> 3. And finally, our ARM team is using the new VMCALL-based hypercall and
> have provided a patch that enables the vm_event on ARM. This will
> require some work with Tamas since it is my suspicion that there's code
> there that should become common between x86 and ARM and has been, at the
> moment, more or less copied from x86 (basically xen/arch/arm/event.c and
> xen/arch/arm/monitor.c).
> 
> The question is, would it be appropriate to add those patches to V3? And
> if that's not a problem, how likely is that to affect the current series
> getting in before the 4.6 release (that is, assuming that's a realistic
> goal, seeing how the feature freeze is two weeks away)? Just trying to
> make sure that I go about this the right way.
> 

Not speaking from technical point of view but from the time scale point
of view, I don't think you should rush your 3 new patches at this stage.

You sent several patch series. I don't have the expertise or time to
keep track of all of them so I couldn't tell how feasible it is for them
to be ready for 4.6. I tend to say if they are not nearly all acked,
they would need to wait until 4.7.

Wei.

> 
> Thanks,
> Razvan

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