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

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 )
      * 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.


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