RE: [Xen-ia64-devel] [PATCH] xen might misunderstand a normal page asI/O page

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

Hi kouya,

I understand now, good catch.
Thanks for your explanation

- Anthony

Kouya SHIMURA write on 2007年1月24日 17:43:
> 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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