Re: [Xen-devel] [PATCH V3] x86/vm_event: block interrupt injection for sync vm_events

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 1/14/19 4:42 PM, Juergen Gross wrote:
> On 14/01/2019 11:56, Razvan Cojocaru wrote:
> > On 1/14/19 11:53 AM, Jan Beulich wrote:
> > > > > > On 14.01.19 at 10:34, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> > > > On 1/12/19 12:04 AM, Boris Ostrovsky wrote:
> > > > > On 12/14/18 6:49 AM, Razvan Cojocaru wrote:
> > > > > > Block interrupts (in vmx_intr_assist()) for the duration of
> > > > > > processing a sync vm_event (similarly to the strategy
> > > > > > currently used for single-stepping). Otherwise, attempting
> > > > > > to emulate an instruction when requested by a vm_event
> > > > > > reply may legitimately need to call e.g.
> > > > > > hvm_inject_page_fault(), which then overwrites the active
> > > > > > interrupt in the VMCS.
> > > > > >
> > > > > > The sync vm_event handling path on x86/VMX is (roughly):
> > > > > > monitor_traps() -> process vm_event -> vmx_intr_assist()
> > > > > > (possibly writing VM_ENTRY_INTR_INFO) ->
> > > > > > hvm_vm_event_do_resume() -> hvm_emulate_one_vm_event()
> > > > > > (possibly overwriting the VM_ENTRY_INTR_INFO value).
> > > > > >
> > > > > > This patch may also be helpful for the future removal
> > > > > > of may_defer in hvm_set_cr{0,3,4} and hvm_set_msr().
> > > > > >
> > > > > > Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> > > > >
> > > > > Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > > > Thanks! So now we have three reviewed-bys, if I'm not mistaken all we
> > > > need is Tamas' (for the vm_event part) and Julien / Stefano's (for ARM)
> > > > acks (or otherwise).
> > > And you'd need to talk Jürgen into allowing this in, now that we're
> > > past the freeze point.
> > (Adding Jürgen to the conversation.)
> >
> > Right, that would be ideal if possible - the code has absolutely no
> > impact on anything unless vm_event is active on the domain, which is
> > never the case for the use-cases considered for a Xen release.
> >
> > So the case I'm making for the patch to go in 4.12 is that:
> >
> > 1. It's perfectly harmless (it affects nothing, except for introspection).
> >
> > 2. It's trivial and thus very easy to see that it's correct.
> >
> > 3. It fixes a major headache for us, and thus it is a great improvement
> > from an introspection standpoint (fixes OS crashes / hangs which we'd
> > otherwise need to work around in rather painful ways).
> >
> > 4. V3 of the patch has been sent out on Dec 14th - it's just that
> > reviewers have had other priorities and it did not gather all acks in time.
> >
> > However, if it's not possible or desirable to allow this in the next
> > best thing is to at least have all the acks necessary for it to go in
> > first thing once the freeze is over.
> >
> >  From Julien's reply I understand that the last ack necessary is Tamas'.
> With that ack just arrived:
>
> Release-acked-by: Juergen Gross <jgross@xxxxxxxx>
Thanks! Very much appreciated.


Razvan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel