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

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

Hi, 

(Assume VPID is available and enabled.)

I'm trying to figure the TLB stuff with VPIDs. I understand from the
poorly written chapter in the intel manual that if an HVM vcpu is running
then only the TLBs tagged with the vcpu.VPID will be used. If xen
or a PV guest is running, then VPID 0 TLBs are what will be used. 

Now I understand the hvm_asid_flush_vcpu upon new guest cr3, will jsut
create a new asid/vpid, so the older vcpu.vpid tlb entries will just not
be used.

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? 

thanks
Mukesh



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