Re: [Xen-devel] [PATCH 4/8] x86/hyperv: setup hypercall page

[Wei Liu <wl@xxxxxxx>]

On Mon, Dec 30, 2019 at 12:55:22PM +0000, Andrew Cooper wrote:
> On 29/12/2019 18:33, Wei Liu wrote:
> > @@ -71,6 +72,40 @@ const struct hypervisor_ops *__init hyperv_probe(void)
> >      return &ops;
> >  }
> >  
> > +static void __init setup_hypercall_page(void)
> > +{
> > +    union hv_x64_msr_hypercall_contents hypercall_msr;
> > +
> > +    /* Unfortunately there isn't a really good way to unwind Xen to
> > +     * not use Hyper-V hooks, so panic if anything goes wrong.
> > +     *
> > +     * In practice if page allocation fails this early on it is
> > +     * unlikely we can get a working system later.
> > +     */
> > +    hv_hypercall_page = alloc_domheap_page(NULL, 0);
> > +    if ( !hv_hypercall_page )
> > +        panic("Failed to allocate Hyper-V hypercall page\n");
> > +
> > +    hv_hypercall = __map_domain_page_global(hv_hypercall_page);
> > +    if ( !hv_hypercall )
> > +        panic("Failed to map Hyper-V hypercall page\n");
> 
> I really hope this doesn't actually function correctly.  This should
> result in an NX mapping.
> 

Ah, stupid me. I had actually looked at Xen's implementation and thought
"wouldn't it be nice to save one page in the image". I clearly missed
that __map_domain_page_global makes the page NX.

Wei.

> See feedback on the next patch for an alternative suggestion.
> 
> ~Andrew

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