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 13:44:12 +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 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?

Thanks,
-Christoffer

> > 
> > What am I missing here?
> > 
> > Cheers,
> > Andre.
> > 
> >> Signed-off-by: Eric Auger <eric.auger@...hat.com>
> >>
> >> ---
> >>
> >> need to CC stable
> >> ---
> >>  virt/kvm/arm/vgic/vgic-its.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> >> index fbbc97b..76bed2d 100644
> >> --- a/virt/kvm/arm/vgic/vgic-its.c
> >> +++ b/virt/kvm/arm/vgic/vgic-its.c
> >> @@ -1329,7 +1329,7 @@ static void vgic_mmio_write_its_cwriter(struct kvm *kvm, struct vgic_its *its,
> >>  
> >>  	reg = update_64bit_reg(its->cwriter, addr & 7, len, val);
> >>  	reg = ITS_CMD_OFFSET(reg);
> >> -	if (reg >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >> +	if (reg && reg >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >>  		mutex_unlock(&its->cmd_lock);
> >>  		return;
> >>  	}
> >> @@ -1370,7 +1370,7 @@ static int vgic_mmio_uaccess_write_its_creadr(struct kvm *kvm,
> >>  	}
> >>  
> >>  	cmd_offset = ITS_CMD_OFFSET(val);
> >> -	if (cmd_offset >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >> +	if (cmd_offset && cmd_offset >= ITS_CMD_BUFFER_SIZE(its->cbaser)) {
> >>  		ret = -EINVAL;
> >>  		goto out;
> >>  	}
> >>