linux-kernel - Re: [PATCH] x86/extable: include asm/processor.h for cpu

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Message-ID: <aAJHMnQPl5iRO5wy@google.com>
Date: Fri, 18 Apr 2025 14:36:02 +0200
From: Dmytro Maluka <dmaluka@...omium.org>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Yue Haibing <yuehaibing@...wei.com>,
	"open list:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/extable: include asm/processor.h for cpu_relax()

On Fri, Apr 18, 2025 at 02:12:03PM +0200, Borislav Petkov wrote:
> On Fri, Apr 18, 2025 at 11:57:00AM +0000, Dmytro Maluka wrote:
> > Include asm/processor.h to prevents compilation failures due to implicit
> > declaration of cpu_relax() in ex_handler_msr_mce() when compiling with
> > CONFIG_X86_MCE disabled.
> 
> Builds fine here:
> 
> $ grep X86_MCE .config
> # CONFIG_X86_MCE is not set
> 
> $ make -j...
> ...
> 
>   OBJCOPY arch/x86/boot/setup.bin
>   BUILD   arch/x86/boot/bzImage
> Kernel: arch/x86/boot/bzImage is ready  (#1)
> $

Yeah, I meant precisely: when compiling with CONFIG_X86_MCE disabled and
some code enabled that includes asm/extable.h without prior including
asm/processor.h.

I encountered that with the out-of-tree-yet code [1] (which is a part of
a prototype implementation of pKVM on x86) which includes asm/sections.h
which includes asm/extable.h.

[1] https://github.com/intel-staging/pKVM-IA/blob/pvVMCS-POC-v6.12/arch/x86/kvm/pkvm/smp.c