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

["Li, Liang Z" <liang.z.li@xxxxxxxxx>]

> -----Original Message-----
> From: Tim Deegan [mailto:tim@xxxxxxx]
> Sent: Thursday, June 11, 2015 10:20 PM
> To: Li, Liang Z
> Cc: xen-devel@xxxxxxxxxxxxx; keir@xxxxxxx; jbeulich@xxxxxxxx;
> andrew.cooper3@xxxxxxxxxx; Tian, Kevin; Zhang, Yang Z
> Subject: Re: [RESEND] nested EPT: fix the handling of nested EPT.
> 
> 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.  I will do test this time ....

> Thanks
> Tim.


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