Re: [Xen-ia64-devel] [PATCH]: vcpu_match_tr_entry & vcpu_ptc_ga

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Thu, Mar 30, 2006 at 04:13:31PM +0100, Tristan Gingold wrote:

> after re-reading code, I think the only possible race is here:
>
>       if (/* is_data && */ vcpu_match_tr_entry(trp,address,rid)) {
>               if (vcpu->domain==dom0 && !in_tpa) *pteval = trp->page_flags;
>
> Do you agree ?

I think so.


> Maybe which should force the p bit on pteval ?

I guess such a trick doesn't solve the problem.
The essential problem is that xen's software tlb cache(vcpu->arch.dtlb)
and physical cpu tlb cache aren't updated atomically.


        CPU0                            CPU1

        a domain issues ptc.ga          a domain issues a access

                                        ia64_do_page_fault()
                                          vcpu_translate()
                                          vcpu->arch.dtlb cache hit.

        vcpu_ptc_ga()
        ia64_global_tlb_purge()
                                        vcpu->rach.dtlb is purged somehow

                                          vcpu_translate() returns
                                          IA64_NO_FAULT

                                          translate_domain_pte()
                                          vcpu_itc_no_srlz()
                                            tlb insert
                                            re-cache vcpu->arch.dtlb
                                            vhpt update

                                         tlb cache entry which should
                                         be purged remains.


                                        domain's access succeeds without
                                        domain seeing fault.


                                        synchronization


                                        a domain again issues access and
                                        succeeds without seeing faults.
                                        However this access should result
                                        in fault.

--
yamahata

_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel