Re: [Xen-devel] [PATCH 11/13] x86/paravirt: Add paravirt alternatives infrastructure

[Josh Poimboeuf <jpoimboe@xxxxxxxxxx>]

On Fri, Oct 06, 2017 at 11:29:52AM -0400, Boris Ostrovsky wrote:
> >>> +
> >>>  void __init_or_module apply_paravirt(struct paravirt_patch_site *start,
> >>>                                struct paravirt_patch_site *end)
> >>>  {
> >>> diff --git a/arch/x86/kernel/cpu/hypervisor.c 
> >>> b/arch/x86/kernel/cpu/hypervisor.c
> >>> index 4fa90006ac68..17243fe0f5ce 100644
> >>> --- a/arch/x86/kernel/cpu/hypervisor.c
> >>> +++ b/arch/x86/kernel/cpu/hypervisor.c
> >>> @@ -71,6 +71,8 @@ void __init init_hypervisor_platform(void)
> >>>   if (!x86_hyper)
> >>>           return;
> >>>  
> >>> + apply_pv_alternatives();
> >> Not for Xen PV guests who have already done this.
> > I think it would be harmless, but yeah, it's probably best to only write
> > it once.
> 
> I also wonder whether calling apply_pv_alternatives() here before
> x86_hyper->init_platform() will work since the latter may be setting
> those op. In fact, that's what Xen HVM does for pv_mmu_ops.exit_mmap.

apply_pv_alternatives() changes:

  (native code)

to

  call *pv_whatever_ops.whatever

So apply_pv_alternatives() should be called *before* any of the ops are
set up.

-- 
Josh

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