Re: [Xen-devel] [RESEND] nested EPT: fix the handling of nested EPT.

[Tim Deegan <tim@xxxxxxx>]

At 07:41 +0000 on 05 Jun (1433490064), Li, Liang Z wrote:
> > -----Original Message-----
> > From: Tim Deegan [mailto:tim@xxxxxxx]
> > At 05:06 +0800 on 03 Jun (1433307971), Liang Li wrote:
> > > If the host EPT entry is changed, the nested EPT should be updated.
> > > The current code does not do this, and it's wrong.
> > >
> > > Reported-by: Tim Deegan <tim@xxxxxxx>
> > > Signed-off-by: Liang Li <liang.z.li@xxxxxxxxx>
> > > Signed-off-by: Yang Zhang <yang.z.zhang@xxxxxxxxx>
> > > ---
> > >  xen/arch/x86/mm/p2m-ept.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > >
> > > diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> > > index 5133eb6..26293a0 100644
> > > --- a/xen/arch/x86/mm/p2m-ept.c
> > > +++ b/xen/arch/x86/mm/p2m-ept.c
> > > @@ -26,6 +26,7 @@
> > >  #include <asm/p2m.h>
> > >  #include <asm/hvm/vmx/vmx.h>
> > >  #include <asm/hvm/vmx/vmcs.h>
> > > +#include <asm/hvm/nestedhvm.h>
> > >  #include <xen/iommu.h>
> > >  #include <asm/mtrr.h>
> > >  #include <asm/hvm/cacheattr.h>
> > > @@ -1076,6 +1077,9 @@ void ept_sync_domain(struct p2m_domain *p2m)
> > >
> > >      ASSERT(local_irq_is_enabled());
> > >
> > > +    if ( nestedhvm_enabled(d) )
> > > +        p2m_flush_nestedp2m(d);
> > 
> > 
> > It seems like this should trigger when the nested EPT table itself is being
> > populated, e.g.
> > 
> >   hvm_hap_nested_page_fault
> >   --> nestedhvm_hap_nested_page_fault
> >   --> nestedhap_fix_p2m (--> p2m_lock(p2m))
> >   --> p2m_set_entry
> >   --> ept_set_entry
> >   --> ept_sync_domain
> >   --> p2m_flush_nestedp2m
> >   --> p2m_flush_table (--> p2m_lock(p2m))
> > 
> > which would deadlock on the nested table's p2m lock.  What have I missed?
> 
> Yes, you are right. 
> 
> Maybe we should add another condition checking, just like:
> 
> struct vcpu *v = current;
> 
> If(nestedhvm_enabled(d)  && !nestedhvm_vcpu_in_guestmode(v) )  
>     p2m_flush_nestedp2m(d);
> 
> 
> Or add a flag(is_nested_p2m) in the struct p2m_domain to mark a nested EPT, 
> and 
> change the condition to:
>       If(nestedhvm_enabled(d)  && p2m->is_nested_p2m )  

Yes, I think this is the right check, but you shouldn't need to add
any new flags: p2m_is_nestedp2m(p2m) will work.

Also, in the next version of the patch, please describe what testing
you've done.

Thanks

Tim.


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel