linux-kernel - Re: [PATCH v2] x86/speculation: Simplify and make CALL

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Message-ID: <20250228164839.ftlvp7iywjenqhlw@desk>
Date: Fri, 28 Feb 2025 08:48:39 -0800
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: x86@...nel.org, Josh Poimboeuf <jpoimboe@...nel.org>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] x86/speculation: Simplify and make CALL_NOSPEC
 consistent

On Fri, Feb 28, 2025 at 10:36:43AM +0100, Ingo Molnar wrote:
> 
> * Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote:
> 
> > CALL_NOSPEC macro is used to generate Spectre-v2 mitigation friendly
> > indirect branches. At compile time the macro defaults to indirect branch,
> > and at runtime those can be patched to thunk based mitigations.
> >
> > This approach is opposite of what is done for the rest of the kernel, where
> > the compile time default is to replace indirect calls with retpoline thunk
> > calls.
> > 
> > Make CALL_NOSPEC consistent with the rest of the kernel, default to
> > retpoline thunk at compile time when CONFIG_MITIGATION_RETPOLINE is
> > enabled.
> > 
> > Also add the missing __CS_PREFIX to the CALL_NOSPEC macro to make it
> > compatible with -mindirect-branch-cs-prefix.
> 
> The __CS_PREFIX change should probably be a separate patch.

Yes, I will split it into a separate patch.