Re: [Xen-devel] [PATCH] Xen 4.4-rc3 regression with PVH compared to Xen 4.4-rc2.

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Mon, 3 Feb 2014 14:53:58 -0500
Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> wrote:

> On Mon, Feb 03, 2014 at 11:26:05AM -0800, Mukesh Rathor wrote:
> > On Mon,  3 Feb 2014 12:03:20 -0500
> > Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx> wrote:
> > 
> > > I am hereby requesting an Xen 4.4 exemption for this bug-fix.
> > > 
> > > The PVH feature is considered experimental, but it would be good
> > > to have it working out of the box without crashing the hypervisor.
> > > 
> > > Sadly that is not the case as
> > > 09bb434748af9bfe3f7fca4b6eef721a7d5042a4 "Nested VMX: prohibit
> > > virtual vmentry/vmexit during IO emulation" casues an NULL
> > > pointer dereference when starting a guest with 'pvh=1' in the
> > > guest config.
> > > 
> > > There are two ways of fixing this:
> > > a). Add an '!xen_pvh_domain()' or '!xen_pvh_vcpu(current)' in the
> > > path, or b). Check for ioreq() being NULL. This is actually done
> > > in other places in the hypervisor - so I choose to piggyback on
> > > that.
> > > 
> > 
> > I was about to send this patch on friday:
> > 
> > diff --git a/xen/arch/x86/hvm/vmx/vvmx.c
> > b/xen/arch/x86/hvm/vmx/vvmx.c index d2ba435..563b02f 100644
> > --- a/xen/arch/x86/hvm/vmx/vvmx.c
> > +++ b/xen/arch/x86/hvm/vmx/vvmx.c
> > @@ -1394,13 +1394,14 @@ void nvmx_switch_guest(void)
> >      struct vcpu *v = current;
> >      struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v);
> >      struct cpu_user_regs *regs = guest_cpu_user_regs();
> > +    ioreq_t *ioreq = get_ioreq(v);
> >  
> >      /*
> >       * a pending IO emualtion may still no finished. In this case,
> >       * no virtual vmswith is allowed. Or else, the following IO
> >       * emulation will handled in a wrong VCPU context.
> >       */
> > -    if ( get_ioreq(v)->state != STATE_IOREQ_NONE )
> > +    if ( ioreq && ioreq->state != STATE_IOREQ_NONE )
> >          return;
> >      /*
> >       * a softirq may interrupt us between a virtual vmentry is
> > 
> > 
> > 
> > when I realized even after the above fix it is still crashing  for
> > me... debugging right now. JFYI.
> 
> Are you doing it on a 'virgin' 4.4-rc3 or with your extra patches?

Actually, it's with my extra dom0 patches.

Mukesh


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