linux-kernel - Re: [PATCH v2 05/10] KVM: arm/arm64: vgic-its: Check GITS_CBASER validity before processing commands

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Date:   Fri, 6 Oct 2017 17:29:09 +0200
From:   Auger Eric <eric.auger@...hat.com>
To:     Andre Przywara <andre.przywara@....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 05/10] KVM: arm/arm64: vgic-its: Check GITS_CBASER
 validity before processing commands

Hi Andre,

On 06/10/2017 16:38, Andre Przywara wrote:
> Hi,
> 
> On 27/09/17 14:28, 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.
> 
> Good catch, but actually it goes a bit further:
> 
> "When GITS_CTLR.Enabled is written from 0 to 1 behavior is UNPREDICTABLE
> if any of the following conditions are true:
> · GITS_CBASER.Valid == 0.
> ...
> "
> 
> So I think we need to check it upon setting CTLR.Enabled.
> I did this in Xen, but forgot to fix this in KVM as well:
> https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=xen/arch/arm/vgic-v3-its.c;hb=HEAD#l1164

OK. I will add this check.

Thanks

Eric
> 
> Cheers,
> Andre.
> 
>>
>> 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 60ecf91..720552c 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)))
>>  		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
>>