linux-kernel - Re: [PATCH v6 01/11] x86/paravirt: Move halt paravirt calls under CONFIG

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Date:   Fri, 3 Sep 2021 20:22:08 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        VMware Inc <pv-drivers@...are.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 01/11] x86/paravirt: Move halt paravirt calls under
 CONFIG_PARAVIRT

On Fri, Sep 03, 2021 at 10:28:02AM -0700, Kuppuswamy Sathyanarayanan wrote:
> diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h
> index c5ce9845c999..ddc77c95adc6 100644
> --- a/arch/x86/include/asm/irqflags.h
> +++ b/arch/x86/include/asm/irqflags.h
> @@ -59,27 +59,8 @@ static inline __cpuidle void native_halt(void)
>  
>  #endif
>  
> -#ifdef CONFIG_PARAVIRT_XXL
> -#include <asm/paravirt.h>
> -#else
> +#ifndef CONFIG_PARAVIRT
>  #ifndef __ASSEMBLY__
> -#include <linux/types.h>
> -
> -static __always_inline unsigned long arch_local_save_flags(void)
> -{
> -	return native_save_fl();
> -}
> -
> -static __always_inline void arch_local_irq_disable(void)
> -{
> -	native_irq_disable();
> -}
> -
> -static __always_inline void arch_local_irq_enable(void)
> -{
> -	native_irq_enable();
> -}
> -
>  /*
>   * Used in the idle loop; sti takes one instruction cycle
>   * to complete:
> @@ -97,6 +78,33 @@ static inline __cpuidle void halt(void)
>  {
>  	native_halt();
>  }
> +#endif /* __ASSEMBLY__ */
> +#endif /* CONFIG_PARAVIRT */
> +
> +#ifdef CONFIG_PARAVIRT
> +#ifndef __ASSEMBLY__
> +#include <asm/paravirt.h>
> +#endif /* __ASSEMBLY__ */
> +#endif /* CONFIG_PARAVIRT */

I think the way we write those is like this:

#ifdef CONFIG_PARAVIRT

# ifndef __ASSEMBLY__
# include <asm/paravirt.h>
# endif

#else /* ! CONFIG_PARAVIRT */

# ifndef __ASSEMBLY__
/*
 * Used in the idle loop; sti takes one instruction cycle
 * to complete:
 */
static inline __cpuidle void arch_safe_halt(void)
{
	native_safe_halt();
}

/*
 * Used when interrupts are already enabled or to
 * shutdown the processor:
 */
static inline __cpuidle void halt(void)
{
	native_halt();
}
# endif /* __ASSEMBLY__ */

#endif /* CONFIG_PARAVIRT */

Note the empty space after the '#' of the inner ifdef to show that it is
an inner one.

Also, this header has clearly too many #if*def __ASSEMBLY__ things
sprinkled around. Lemme see if I can get rid of them so that it is at
least a bit readable.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette