From mboxrd@z Thu Jan  1 00:00:00 1970
From: Dave Martin <Dave.Martin@arm.com>
Subject: Re: [PATCH 1/3] arm64: KVM: Move CPU ID reg trap setup off the world
 switch path
Date: Wed, 6 Dec 2017 11:55:01 +0000
Message-ID: <20171206115501.GB22781@e103592.cambridge.arm.com>
References: <1512141582-17474-1-git-send-email-Dave.Martin@arm.com>
 <1512141582-17474-2-git-send-email-Dave.Martin@arm.com>
 <20171205090915.GI32397@cbox>
 <20171205123150.GX22781@e103592.cambridge.arm.com>
 <20171206105300.GK32397@cbox>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <kvmarm-bounces@lists.cs.columbia.edu>
Received: from localhost (localhost [127.0.0.1])
 by mm01.cs.columbia.edu (Postfix) with ESMTP id 7D07A49D28
 for <kvmarm@lists.cs.columbia.edu>; Wed,  6 Dec 2017 06:51:54 -0500 (EST)
Received: from mm01.cs.columbia.edu ([127.0.0.1])
 by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024)
 with ESMTP id fM0Zj90MKc+f for <kvmarm@lists.cs.columbia.edu>;
 Wed,  6 Dec 2017 06:51:53 -0500 (EST)
Received: from foss.arm.com (foss.arm.com [217.140.101.70])
 by mm01.cs.columbia.edu (Postfix) with ESMTP id 544C640651
 for <kvmarm@lists.cs.columbia.edu>; Wed,  6 Dec 2017 06:51:53 -0500 (EST)
Content-Disposition: inline
In-Reply-To: <20171206105300.GK32397@cbox>
List-Unsubscribe: <https://lists.cs.columbia.edu/mailman/options/kvmarm>,
 <mailto:kvmarm-request@lists.cs.columbia.edu?subject=unsubscribe>
List-Archive: <https://lists.cs.columbia.edu/pipermail/kvmarm>
List-Post: <mailto:kvmarm@lists.cs.columbia.edu>
List-Help: <mailto:kvmarm-request@lists.cs.columbia.edu?subject=help>
List-Subscribe: <https://lists.cs.columbia.edu/mailman/listinfo/kvmarm>,
 <mailto:kvmarm-request@lists.cs.columbia.edu?subject=subscribe>
Errors-To: kvmarm-bounces@lists.cs.columbia.edu
Sender: kvmarm-bounces@lists.cs.columbia.edu
To: Christoffer Dall <christoffer.dall@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>, Okamoto Takayuki <tokamoto@jp.fujitsu.com>, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org
List-Id: kvmarm@lists.cs.columbia.edu

On Wed, Dec 06, 2017 at 11:53:00AM +0100, Christoffer Dall wrote:
> On Tue, Dec 05, 2017 at 12:31:51PM +0000, Dave Martin wrote:
> > On Tue, Dec 05, 2017 at 10:09:15AM +0100, Christoffer Dall wrote:
> > > On Fri, Dec 01, 2017 at 03:19:40PM +0000, Dave Martin wrote:
> > > > The HCR_EL2.TID3 flag needs to be set when trapping guest access to
> > > > the CPU ID registers is required.  However, the decision about
> > > > whether to set this bit does not need to be repeated at every
> > > > switch to the guest.
> > > > 
> > > > Instead, it's sufficient to make this decision once and record the
> > > > outcome.
> > > > 
> > > > This patch moves the decision to vcpu_reset_hcr() and records the
> > > > choice made in vcpu->arch.hcr_el2.  The world switch code can then
> > > > load this directly when switching to the guest without the need for
> > > > conditional logic on the critical path.
> > > > 
> > > > Signed-off-by: Dave Martin <Dave.Martin@arm.com>
> > > > Suggested-by: Christoffer Dall <christoffer.dall@linaro.org>
> > > > Cc: Marc Zyngier <marc.zyngier@arm.com>
> > > 
> > > Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
> > > 
> > > > 
> > > > ---
> > > > 
> > > > Note to maintainers: this was discussed on-list [1] prior to the merge
> > > > window, but this patch implementing the agreed decision hasn't been
> > > > posted previously.
> > > > 
> > > > This should be considered a fix for v4.15.
> > > 
> > > It's actually easier for me to apply this for v4.16 and base my VHE
> > > optimization patches on it.
> > 
> > If you're happy for this optimisation to be missing for v4.15, I'm fine
> > with that.
> > 
> > Can I leave it you to pick this up then?
> 
> Yes, I applied it to our queue already.

OK, great, thanks
---Dave