Xen devel - Apr 2006 - RE: [PATCH][RESEND] only BSP can really do clear_all_shadow_status

>On 15 Apr 2006, at 15:54, Li, Xin B wrote:
>
>> only BSP can really do clear_all_shadow_status.
>> This fixes SMP IA32 VMX guest booting on IA32 xen.
>
>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.

For long term, maybe we will move to per vcpu shadow.

-Xin

>
>  -- Keir
>
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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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