Re: [Xen-devel] Question about VPID during MOV-TO-CR3

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 22.09.16 at 19:18, <tamas.lengyel@xxxxxxxxxxxx> wrote:
> So I verified that when CPU-based load exiting is enabled, the TLB
> flush here is critical. Without it the guest kernel crashes at random
> points during boot. OTOH why does Xen trap every guest CR3 update
> unconditionally? While we have features such as the vm_event/monitor
> that may choose to subscribe to that event, Xen traps it even when
> that is not in use. Is that trapping necessary for something else?

Where do you see this being unconditional? construct_vmcs()
clearly avoids setting these intercepts when using EPT. Are you
perhaps suffering from

            /* Trap CR3 updates if CR3 memory events are enabled. */
            if ( v->domain->arch.monitor.write_ctrlreg_enabled &
                 monitor_ctrlreg_bitmask(VM_EVENT_X86_CR3) )
                v->arch.hvm_vmx.exec_control |= CPU_BASED_CR3_LOAD_EXITING;

in vmx_update_guest_cr()? That'll be rather something for you
or Razvan to explain. Outside of nested VMX I don't see any
other enabling of that intercept (didn't check AMD code on the
assumption that you're working on Intel hardware).

Jan


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