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 13:54:34 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoffer Dall <cdall@...aro.org>
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

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.

Thanks

Eric
> 
> 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;
>>>>  	}
>>>>