linux-kernel - Re: [PATCH 1/9] KVM: arm64: vgic-v3: Fix some error codes when setting RDIST base

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Date:   Thu, 14 Jan 2021 11:02:55 +0100
From:   Auger Eric <eric.auger@...hat.com>
To:     Alexandru Elisei <alexandru.elisei@....com>,
        eric.auger.pro@...il.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, kvmarm@...ts.cs.columbia.edu, maz@...nel.org,
        drjones@...hat.com
Cc:     james.morse@....com, julien.thierry.kdev@...il.com,
        suzuki.poulose@....com, shuah@...nel.org, pbonzini@...hat.com
Subject: Re: [PATCH 1/9] KVM: arm64: vgic-v3: Fix some error codes when
 setting RDIST base

Hi Alexandru,

On 1/6/21 5:32 PM, Alexandru Elisei wrote:
> Hi Eric,
> 
> On 12/12/20 6:50 PM, Eric Auger wrote:
>> KVM_DEV_ARM_VGIC_GRP_ADDR group doc says we should return
>> -EEXIST in case the base address of the redist is already set.
>> We currently return -EINVAL.
>>
>> However we need to return -EINVAL in case a legacy REDIST address
>> is attempted to be set while REDIST_REGIONS were set. This case
>> is discriminated by looking at the count field.
>>
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>> ---
>>  arch/arm64/kvm/vgic/vgic-mmio-v3.c | 9 +++++++--
>>  1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/kvm/vgic/vgic-mmio-v3.c b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> index 15a6c98ee92f..8e8a862def76 100644
>> --- a/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> +++ b/arch/arm64/kvm/vgic/vgic-mmio-v3.c
>> @@ -792,8 +792,13 @@ static int vgic_v3_insert_redist_region(struct kvm *kvm, uint32_t index,
>>  	int ret;
>>  
>>  	/* single rdist region already set ?*/
>> -	if (!count && !list_empty(rd_regions))
>> -		return -EINVAL;
>> +	if (!count && !list_empty(rd_regions)) {
>> +		rdreg = list_last_entry(rd_regions,
>> +				       struct vgic_redist_region, list);
>> +		if (rdreg->count)
>> +			return -EINVAL; /* Mixing REDIST and REDIST_REGION API */
>> +		return -EEXIST;
>> +	}
> 
> A few instructions below:
> 
>     if (list_empty(rd_regions)) {
>         [..]
>     } else {
>         rdreg = list_last_entry(rd_regions,
>                     struct vgic_redist_region, list);
>         [..]
> 
>         /* Cannot add an explicitly sized regions after legacy region */
>         if (!rdreg->count)
>             return -EINVAL;
>     }
> 
> Isn't this testing for the same thing, but using the opposite condition? Or am I
> misunderstanding the code (quite likely)?
the 1st test sequence handles the case where the legacy
KVM_VGIC_V3_ADDR_TYPE_REDIST is used (!count) while the second handles
the case where the REDIST_REGION is used. Nevertheless I think this can
be simplified into:

        if (list_empty(rd_regions)) {
                if (index != 0)
                        return -EINVAL;
        } else {
                rdreg = list_last_entry(rd_regions,
                                        struct vgic_redist_region, list);

                if ((!count) != (!rdreg->count))
                        return -EINVAL; /* Mix REDIST and REDIST_REGION */

                if (!count)
                        return -EEXIST;

                if (index != rdreg->index + 1)
                        return -EINVAL;
        }






> 
> Looks to me like KVM_DEV_ARM_VGIC_GRP_ADDR(KVM_VGIC_V3_ADDR_TYPE_REDIST{,_REGION})
> used to return -EEXIST (from vgic_check_ioaddr()) before commit ccc27bf5be7b7
> ("KVM: arm/arm64: Helper to register a new redistributor region") which added the
> vgic_v3_insert_redist_region() function, so bringing back the -EEXIST return code
> looks the right thing to me.

OK thank you for the detailed study.

Eric
> 
> Thanks,
> Alex
>>  
>>  	/* cross the end of memory ? */
>>  	if (base + size < base)
>