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

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Date:   Fri, 6 Oct 2017 15:37:37 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Eric Auger <eric.auger@...hat.com>, eric.auger.pro@...il.com,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        marc.zyngier@....com, cdall@...aro.org, peter.maydell@...aro.org,
        wanghaibin.wang@...wei.com
Cc:     wu.wubin@...wei.com
Subject: Re: [PATCH v2 02/10] KVM: arm/arm64: vgic-its: Always allow clearing
 GITS_CREADR/CWRITER

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.

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;
>  	}
>