linux-kernel - Re: [PATCH] x86/apic: simplify disconnect_bsp

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Message-ID: <20200219123650.GL3886@Air-de-Roger>
Date:   Wed, 19 Feb 2020 13:36:50 +0100
From:   Roger Pau Monné <roger.pau@...rix.com>
To:     <linux-kernel@...r.kernel.org>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Tony Luck <tony.luck@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Jan Beulich <jbeulich@...e.com>,
        "Sean Christopherson" <sean.j.christopherson@...el.com>
Subject: Re: [PATCH] x86/apic: simplify disconnect_bsp_APIC setup of LVT{0/1}

Ping?

On Mon, Jan 27, 2020 at 06:57:58PM +0100, Roger Pau Monne wrote:
> There's no need to read the current values of LVT{0/1} for the
> purposes of the function, which seem to be to save the currently
> selected vector: in the destination modes used (ExtINT and NMI) the
> vector field is ignored and hence can be set to 0.
> 
> Note that clear_local_APIC as called by init_bsp_APIC would have
> already wiped those registers by writing APIC_LVT_MASKED, and hence
> there's nothing useful to preserve if that was the intent. Also note
> that there are other places where LVT{0/1} is written to without doing
> a read-modify-write (init_bsp_APIC and clear_local_APIC), so if
> writing 0s to the reserved parts would cause issues they would be also
> triggered by writes elsewhere.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>
> ---
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: x86@...nel.org
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Tony Luck <tony.luck@...el.com>
> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Cc: Kefeng Wang <wangkefeng.wang@...wei.com>
> Cc: Jan Beulich <jbeulich@...e.com>
> Cc: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kernel/apic/apic.c | 14 ++------------
>  1 file changed, 2 insertions(+), 12 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
> index 28446fa6bf18..ce0c65340b4c 100644
> --- a/arch/x86/kernel/apic/apic.c
> +++ b/arch/x86/kernel/apic/apic.c
> @@ -2292,12 +2292,7 @@ void disconnect_bsp_APIC(int virt_wire_setup)
>  		 * For LVT0 make it edge triggered, active high,
>  		 * external and enabled
>  		 */
> -		value = apic_read(APIC_LVT0);
> -		value &= ~(APIC_MODE_MASK | APIC_SEND_PENDING |
> -			APIC_INPUT_POLARITY | APIC_LVT_REMOTE_IRR |
> -			APIC_LVT_LEVEL_TRIGGER | APIC_LVT_MASKED);
> -		value |= APIC_LVT_REMOTE_IRR | APIC_SEND_PENDING;
> -		value = SET_APIC_DELIVERY_MODE(value, APIC_MODE_EXTINT);
> +		value = APIC_LVT_REMOTE_IRR | APIC_SEND_PENDING | APIC_DM_EXTINT;
>  		apic_write(APIC_LVT0, value);
>  	} else {
>  		/* Disable LVT0 */
> @@ -2308,12 +2303,7 @@ void disconnect_bsp_APIC(int virt_wire_setup)
>  	 * For LVT1 make it edge triggered, active high,
>  	 * nmi and enabled
>  	 */
> -	value = apic_read(APIC_LVT1);
> -	value &= ~(APIC_MODE_MASK | APIC_SEND_PENDING |
> -			APIC_INPUT_POLARITY | APIC_LVT_REMOTE_IRR |
> -			APIC_LVT_LEVEL_TRIGGER | APIC_LVT_MASKED);
> -	value |= APIC_LVT_REMOTE_IRR | APIC_SEND_PENDING;
> -	value = SET_APIC_DELIVERY_MODE(value, APIC_MODE_NMI);
> +	value = APIC_LVT_REMOTE_IRR | APIC_SEND_PENDING | APIC_DM_NMI;
>  	apic_write(APIC_LVT1, value);
>  }
>  
> -- 
> 2.25.0
>