Re: [V1 PATCH 1/3] pvh: early return from hvm_hap_nested_page_fault

[Mukesh Rathor <mukesh.rathor@oracle.com>]

On Thu, 27 Feb 2014 11:56:05 +0100
Tim Deegan <tim@xen.org> wrote:

> At 17:03 -0800 on 24 Feb (1393257835), Mukesh Rathor wrote:
> > pvh does not support nested hvm at present. As such, return if pvh.
> 
> Nack, sorry.  
> 
> 1: this is the nested pagefault (i.e. EPT/NPT) handler, not part of
> the nested HVM code.

yeah, jan already pointed that out. i just quickly whipped it out last
minute after seeing a crash in hvm_hap_nested_page_fault from running
xentrace on pvh. anyways, i'll take a look at it.

> 2: If there _is_ a problem with the interaction between nested HVM and
> PVH, the right way to fix it is to enforce that they can't both be
> enabled at the same time, and then make sure all the nested-HVM code
> properly checks for being enabled.  It's not a good idea to scatter
> PVH checks all over code for unrelated features.

Yup. thanks.

Mueksh

> 
> > Signed-off-by: Mukesh Rathor <mukesh.rathor@oracle.com>
> > ---
> >  xen/arch/x86/hvm/hvm.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> > index 69f7e74..a4a3dcf 100644
> > --- a/xen/arch/x86/hvm/hvm.c
> > +++ b/xen/arch/x86/hvm/hvm.c
> > @@ -1416,6 +1416,9 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
> >      int sharing_enomem = 0;
> >      mem_event_request_t *req_ptr = NULL;
> >  
> > +    if ( is_pvh_vcpu(v) )
> > +        return 0;
> > +
> >      /* On Nested Virtualization, walk the guest page table.
> >       * If this succeeds, all is fine.
> >       * If this fails, inject a nested page fault into the guest.
> > -- 
> > 1.8.3.1
> > 
> > 
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