linux-kernel - Re: [patch 2/3] x86/smpboot: Remove stale tlb flush invocations

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Message-ID: <20171230213231.haifzuhufkoyeaz7@gmail.com>
Date:   Sat, 30 Dec 2017 22:32:31 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...uxfoundation.org>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Borislav Petkov <bp@...en8.de>,
        Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [patch 2/3] x86/smpboot: Remove stale tlb flush invocations


* Thomas Gleixner <tglx@...utronix.de> wrote:

> smpboot_setup_warm_reset_vector() and smpboot_restore_warm_reset_vector()
> invoke local_flush_tlb() for no obvious reason.
> 
> Digging in history revealed that the original code in the 2.1 aera added
> those because the code manipulated a swapper_pg_dir pagetable entry. The
> pagetable manipulation was removed long ago in the 2.3 timeframe, but the
> tlb flush invocations stayed around forever.

s/tlb/TLB

> 
> Remove them along with the pointless pr_debugs which come from the same 2.1
> change.
> 
> Reported-by: Dominik Brodowski <linux@...inikbrodowski.net>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  arch/x86/kernel/smpboot.c |    9 ---------
>  1 file changed, 9 deletions(-)
> 
> --- a/arch/x86/kernel/smpboot.c
> +++ b/arch/x86/kernel/smpboot.c
> @@ -128,14 +128,10 @@ static inline void smpboot_setup_warm_re
>  	spin_lock_irqsave(&rtc_lock, flags);
>  	CMOS_WRITE(0xa, 0xf);
>  	spin_unlock_irqrestore(&rtc_lock, flags);
> -	local_flush_tlb();
> -	pr_debug("1.\n");
>  	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_HIGH)) =
>  							start_eip >> 4;
> -	pr_debug("2.\n");
>  	*((volatile unsigned short *)phys_to_virt(TRAMPOLINE_PHYS_LOW)) =
>  							start_eip & 0xf;
> -	pr_debug("3.\n");
>  }
>  
>  static inline void smpboot_restore_warm_reset_vector(void)
> @@ -143,11 +139,6 @@ static inline void smpboot_restore_warm_
>  	unsigned long flags;
>  
>  	/*
> -	 * Install writable page 0 entry to set BIOS data area.
> -	 */
> -	local_flush_tlb();
> -
> -	/*
>  	 * Paranoid:  Set warm reset code and vector here back
>  	 * to default values.
>  	 */

Really nice archeology! :-)

Reviewed-by: Ingo Molnar <mingo@...nel.org>

Thanks,

	Ingo