[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] RE: about fixup_page_fault
>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx] >Sent: Wednesday, December 17, 2008 4:23 PM > >On 17/12/2008 03:17, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote: > >> I guess I may miss sth important, but I don't understand below >> code at end of fixup_page_fault: >> >> if ( paging_mode_enabled(d) ) >> { >> int ret = paging_fault(addr, regs); >> if ( ret == EXCRET_fault_fixed ) >> trace_trap_two_addr(TRC_PV_PAGING_FIXUP, >regs->eip, addr); >> return ret; >> } >> >> Shouldn't a check upon guest_mode(regs) is required, since the >> fault may be triggered by xen itself? For example, a null pointer >> deference by xen code (not passed from guest) may not get chance >> to reach "fatal page fault" and instead a guest page fault could be >> injected per my reading... > >Consider copy_from_guest() applied to a PV guest with dirty >logging enabled. >The #PF handler should fix up faults when accessing guest >address space via >shadow page tables, even when the access happens within Xen. If Xen access guest address space intentionally like a hypercall parameter, such fix up is desired. However what about an random illegal access in Xen with faulting address happening to fall into guest address space? Thanks, Kevin _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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