Re: [PATCH][RFC] Supporting Enlightened Windows 2008Server

[Tim Deegan <Tim.Deegan@citrix.com>]

At 18:10 -0700 on 06 Mar (1204827047), Ky Srinivasan wrote:

> The Veridian API allows the guest to pass in a variable list of
> arguments to the TLB flush call
> (HvFlushVirtualAddressList). Furthermore, both forms of the flush APIs
> (HvFlushVirtualAddressSpace and HvFlushVirtualAdressList) can specify
> a list of vcpus that should be involved in the flush process.

I expect that the best way to implement the list-of-addresses feature on
Xen is to do a full TLB flush if there's more than one entry in the list
(that's different from the Hyper-V shadow pagetable design, where
explicit lists of addresses to flush make much more sense).

Then all you need are the existing Xen TLB flush operations, and some
means of gating them.  If you use a generation counter with each vcpu's
inhibit bit, you can probably do that without the need for any locks.

> So, as
> you have noted we will need a mechanism to co-ordinate the flush
> operation amongst the set of vcpus involved which means we need to be
> able give up the physical CPU in the hypervisor waiting for the flush
> to complete. I have used wait_on_xen_event_channel() to implement this
> synchronization.

wait_on_xen_event_channel is more than you need, since you're not going
to wake on events.

> Since we don't preserve the stack state when we block
> in the hypervisor, I have used a seperate per-vcpu page for dealing
> with hypercall input parameters for calls that can potentially block
> in the hypervisor.

Xen already has a system of hypercall continuations that might help here.

Cheers,

Tim

-- 
Tim Deegan <Tim.Deegan@citrix.com>
Principal Software Engineer, Citrix Systems (R&D) Ltd.
[Company #02300071, SL9 0DZ, UK.]