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Date: Fri, 6 Oct 2017 11:30:07 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
        Juergen Gross <jgross@suse.com>, Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Sasha Levin <alexander.levin@verizon.com>,
        live-patching@vger.kernel.org, Jiri Slaby <jslaby@suse.cz>,
        Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Peter Zijlstra <peterz@infradead.org>, Mike Galbraith <efault@gmx.de>,
        Chris Wright <chrisw@sous-sol.org>, Alok Kataria <akataria@vmware.com>,
        Rusty Russell <rusty@rustcorp.com.au>,
        virtualization@lists.linux-foundation.org,
        xen-devel@lists.xenproject.org, Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>
Subject: Re: [PATCH 11/13] x86/paravirt: Add paravirt alternatives
 infrastructure
Message-ID: <20171006163007.gm7jqhz2jvxulpn4@treble>
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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