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

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Message-ID: <20200319182727.GN24449@Air-de-Roger.citrite.net>
Date:   Thu, 19 Mar 2020 19:27:27 +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: PING: [PATCH] x86/apic: simplify disconnect_bsp_APIC setup of
 LVT{0/1}

On Wed, Feb 19, 2020 at 01:36:54PM +0100, Roger Pau Monné wrote:
> Ping?

Ping x2.

Thanks.

> 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
> >