Re: [Xen-devel] [help]: VPID tagged TLBs question.

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Thu, 26 Apr 2012 08:23:29 +0100
Keir Fraser <keir.xen@xxxxxxxxx> wrote:

> On 26/04/2012 02:07, "Mukesh Rathor" <mukesh.rathor@xxxxxxxxxx> wrote:
> 
> > However, I don't understand the use of hvm_asid_flush_core which
> > it appears will cause all HVM vcpu's to get new vpid/asid, hence,
> > discard all previously used VPID tagged TLBs. In particular,
> > consider a PV guest:
> > 
> > write_ptbase -> write_cr3 -> hvm_flush_guest_tlbs ->
> > hvm_asid_flush_core().
> > 
> > Since the PV guest is only using VPID 0 tagged TLBs, why do we need
> > to flush all TLBs for all HVM guests?
> 
> It's just being conservative, as callers of write_cr3 may assume that
> the TLB is entirely flushed, for all guests.

Well, for write_cr3 path at least, we just need to invalidate all TLBs
in the local pcpu. So it seems for this path we could just do 
invvpid with type 2, ie, invalidate all vpids except 0. Prob also need
to do 'invept 2'. what do you think, worth it?

thanks,
Mukesh



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