Hi Anthony,
The guest OS can use ig field{63:53} in VHPT Short/Long Format.
Actually Windows seems to use this field and sometimes set bit{60}.
Xen/IPF also uses bit{60} of PTE as VTLB_PTE_IO_BIT.
So misunderstanding may happen.
When first TLB-miss happens, the pteval in a guest VHPT propagates as
follows:
In vmx_hpw_miss(),
=> }else if(type == DSIDE_TLB){
=> if (!guest_vhpt_lookup(vhpt_adr, &pteval)) {
=> thash_purge_and_insert(v, pteval, itir, vadr, DSIDE_TLB);
In thash_purge_and_insert(),
=> if(VMX_DOMAIN(v)){
=> if (ps == mrr.ps) {
=> if(!(pte&VTLB_PTE_IO)){ <<<<< This condition is failure
else{
vtlb_insert(v, pte, itir, ifa);
vcpu_quick_region_set(PSCBX(v,tc_regions),ifa);
}
After all, this TLB-miss wastes a vtlb and reproduce TLB-miss again.
When the second TLB-miss happens,
In vmx_hpw_miss(),
=> if((data=vtlb_lookup(v, vadr,type))!=0){
=> if (v->domain != dom0 && type == DSIDE_TLB) {
=> if (__gpfn_is_io(v->domain, gppa >> PAGE_SHIFT)) { <<<<< failure.
resolve misunderstanding
=> thash_vhpt_insert(v, data->page_flags, data->itir, vadr, type);
My patch just masks the ig field.
Thanks
Kouya
Xu, Anthony writes:
> Hi Kouya,
>
> Can you explain more?
>
> How does misunderstanding happen?
> And how does this patch fix it?
>
> Thanks
> Anthony
>
> Kouya SHIMURA write on 2007年1月24日 12:31:
> > Hi,
> >
> > Hypervisor might misunderstand a normal page as I/O page
> > if a guest OS uses the ig field in the guest VHPT.
> >
> > It seems to be harmless but slightly slow down.
> >
> > Thanks,
> > Kouya
> >
> > Signed-off-by: Kouya Shimura <kouya@xxxxxxxxxxxxxx>
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