linux-kernel - Re: [PATCH v4 06/11] KVM: arm/arm64: vgic-its: Check GITS_CBASER validity before processing commands

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Message-ID: <af19b9bb-02f0-7e6f-6555-7a6d0ce30ef7@redhat.com>
Date:   Wed, 18 Oct 2017 16:34:04 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Christoffer Dall <cdall@...aro.org>
Cc:     eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu,
        marc.zyngier@....com, peter.maydell@...aro.org,
        andre.przywara@....com, wanghaibin.wang@...wei.com,
        wu.wubin@...wei.com, drjones@...hat.com, wei@...hat.com
Subject: Re: [PATCH v4 06/11] KVM: arm/arm64: vgic-its: Check GITS_CBASER
 validity before processing commands

Hi Christoffer,

On 18/10/2017 00:10, Christoffer Dall wrote:
> On Tue, Oct 17, 2017 at 09:10:04AM +0200, Eric Auger wrote:
>> At the moment vgic_its_process_commands() does not
>> check the CBASER is valid before processing any command.
>> Let's fix that.
>>
>> Also rename cbaser local variable into cbaser_pa to avoid
>> any confusion with the full register.
>>
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>> ---
>>  virt/kvm/arm/vgic/vgic-its.c | 13 ++++++++-----
>>  1 file changed, 8 insertions(+), 5 deletions(-)
>>
>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>> index 3b539d4..e18f1e4 100644
>> --- a/virt/kvm/arm/vgic/vgic-its.c
>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>> @@ -1301,17 +1301,20 @@ static void vgic_mmio_write_its_cbaser(struct kvm *kvm, struct vgic_its *its,
>>  /* Must be called with the cmd_lock held. */
>>  static void vgic_its_process_commands(struct kvm *kvm, struct vgic_its *its)
>>  {
>> -	gpa_t cbaser;
>> +	gpa_t cbaser_pa;
>>  	u64 cmd_buf[4];
>>  
>> -	/* Commands are only processed when the ITS is enabled. */
>> -	if (!its->enabled)
>> +	/*
>> +	 * Commands are only processed when the ITS is enabled and
>> +	 * CBASER is valid
>> +	 */
>> +	if (!its->enabled || (!(its->cbaser & GITS_CBASER_VALID)))
> 
> Is it valid to clear the CBASER valid bit after having enabled the ITS?
> If not, I think you should check changes to CBASER and then this
> shouldn't be necessary.

Yes you're right. the spec says:
When GITS_CTLR.Enable == 1 or GITS_CTLR.Quiescent == 0, writing this
register (CBASER) is UNPREDICTABLE .

Given we already check its->enabled in vgic_mmio_write_its_cbaser, I
think it is safe to remove this patch.

Thanks

Eric
> 
> 
> 
>>  		return;
>>  
>> -	cbaser = CBASER_ADDRESS(its->cbaser);
>> +	cbaser_pa = CBASER_ADDRESS(its->cbaser);
>>  
>>  	while (its->cwriter != its->creadr) {
>> -		int ret = kvm_read_guest(kvm, cbaser + its->creadr,
>> +		int ret = kvm_read_guest(kvm, cbaser_pa + its->creadr,
>>  					 cmd_buf, ITS_CMD_SIZE);
>>  		/*
>>  		 * If kvm_read_guest() fails, this could be due to the guest
>> -- 
>> 2.5.5
>>
> 
> Otherwise, this looks fine.
> 
> Thanks,
> -Christoffer
>