[PATCH v2] x86, hyperv: fix kernel panic when kexec on HyperV

[Kairui Song]

On Tue, Mar 5, 2019 at 8:33 PM Peter Zijlstra <peterz at infradead.org> wrote:
>
> On Tue, Mar 05, 2019 at 08:17:03PM +0800, Kairui Song wrote:
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index 7abb09e2eeb8..34aa1e953dfc 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -406,6 +406,12 @@ void hyperv_cleanup(void)
> >       /* Reset our OS id */
> >       wrmsrl(HV_X64_MSR_GUEST_OS_ID, 0);
> >
> > +     /* Cleanup hypercall page reference before reset the page */
> > +     hv_hypercall_pg = NULL;
> > +
> > +     /* Make sure page reference is cleared before wrmsr */
>
> This comment forgets to tell us who cares about this. And why the wrmsr
> itself isn't serializing enough.
>
> > +     wmb();
> > +
> >       /* Reset the hypercall page */
> >       hypercall_msr.as_uint64 = 0;
> >       wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
>
> That looks like a fake MSR; and you're telling me that VMEXIT doesn't
> serialize?

Thanks for the review, seem I being a bit paranoid on this. Will drop
it and send a v3 if no one has any other complaint.

--
Best Regards,
Kairui Song