linux-kernel - Re: [PATCH v2 02/10] KVM: arm/arm64: vgic-its: Always allow clearing GITS

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Date:   Fri, 13 Oct 2017 19:54:46 +0200
From:   Christoffer Dall <cdall@...aro.org>
To:     Auger Eric <eric.auger@...hat.com>
Cc:     Andre Przywara <andre.przywara@....com>, eric.auger.pro@...il.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        marc.zyngier@....com, peter.maydell@...aro.org,
        wanghaibin.wang@...wei.com, wu.wubin@...wei.com
Subject: Re: [PATCH v2 02/10] KVM: arm/arm64: vgic-its: Always allow clearing
 GITS_CREADR/CWRITER

On Fri, Oct 13, 2017 at 01:54:34PM +0200, Auger Eric wrote:
> Hi Christoffer,
> On 13/10/2017 13:44, Christoffer Dall wrote:
> > On Fri, Oct 06, 2017 at 05:29:02PM +0200, Auger Eric wrote:
> >> Hi,
> >>
> >> On 06/10/2017 16:37, Andre Przywara wrote:
> >>> Hi,
> >>>
> >>> On 27/09/17 14:28, Eric Auger wrote:
> >>>> If the GITS_CBASER Size field is 0, which can correspond to a
> >>>> reset value, the userspace fails to set the GITS_CREADR/CWRITER
> >>>> offsets to 0. This failure is not justified.
> >>>>
> >>>> Let's allow this setting which can also correspond to a reset value.
> >>>
> >>> But the GITS_CBASER size field has a +1 encoding, so can never be 0, if
> >>> I understand the manual (and ITS_CMD_BUFFER_SIZE) correctly.
> >> Oh OK, you're. I missed that. I would have sworn I've seen that failure
> >> but I must have misinterpreted it.
> >>
> > 
> > What is CWRITER is written to a brand new ITS before the CBASER is
> > written?
> > 
> > I don't see us initializing the cbaser field anywhere?
> in vgic_its_create() its is allocated with kzalloc so its->cbaser is
> initialized at this moment.
> 

Right, so it can be 0, and we still need your patch, contrary to Andre's
comment.  Am I missing something?

Thanks,
-Christoffer