linux-kernel - Re: [PATCH v3 3/7] x86/bugs: Exit early if return thunk is already set

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Message-ID: <20250528215549.ql33m3tasfxzunbw@desk>
Date: Wed, 28 May 2025 14:55:49 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, David Kaplan <david.kaplan@....com>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
	Josh Poimboeuf <jpoimboe@...nel.org>
Subject: Re: [PATCH v3 3/7] x86/bugs: Exit early if return thunk is already
 set

On Sat, May 24, 2025 at 01:27:29PM +0200, Borislav Petkov wrote:
> On Thu, May 22, 2025 at 06:21:02PM -0700, Pawan Gupta wrote:
> > When the exact same return thunk is already set, avoid the warning and exit
> > early. This is to prepare for ITS to also set CDT return thunk independent
> > of retbleed.
> > 
> > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> > ---
> >  arch/x86/kernel/cpu/bugs.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> > index 94d0de3e61aec32b3b67c8d21f89a8c67b93dff3..354593065025fd7c5727e955d76523777b3da9ee 100644
> > --- a/arch/x86/kernel/cpu/bugs.c
> > +++ b/arch/x86/kernel/cpu/bugs.c
> > @@ -113,6 +113,9 @@ void (*x86_return_thunk)(void) __ro_after_init = __x86_return_thunk;
> >  
> >  static void __init set_return_thunk(void *thunk)
> >  {
> > +	if (thunk == x86_return_thunk)
> > +		return;
> > +
> >  	if (x86_return_thunk != __x86_return_thunk)
> >  		pr_warn("x86/bugs: return thunk changed\n");
> 
> Ok, let's drop those silly conditionals here and simply issue the name. We'll
> see later whether this needs to be louder...

Ok, will do.