[Xen-devel] Re: [PATCH][RESEND] only BSP can really do clear_all_shadow_status

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 15 Apr 2006, at 20:05, Li, Xin B wrote:

> > Why can only VCPU0 do this? Is the argument to
> > clear_all_shadow_status() always current domain? If so that should
> > probably be asserted, or the argument removed.
> Both Jun and I think clear_all_shadow_status is overkilled,
> update_pagetables should have done the cleanup things, so we thought
> about removing it, but the test shows that removing it breaks windows 
> on
> PAE xen, and I'm looking at this issue.
>
> Actually, this patch should be a right direction, and changeset 9626 
> has
> alrealdy changed shadow.c like what this patch does to shadow32.c.
Okay. But weren't we going to *get rid* of shadow32.c at some point? :-)

> For long term, maybe we will move to per vcpu shadow.
I wondered about that but wasn't convinced it'd help with scalability. 
Fundamentally, if VCPU-A updates a guest pte that is in VCPU-B's shadow 
cache, B's shadowed version has to be modified no later than the next 
TLB flush on VCPU-B. So there will still be potentially significant 
synchronisation across shadow caches although maybe some cunningness 
can avoid bad behaviour in most cases.
 -- Keir


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